Unlike in some cars such as VW’s, in a Subaru, the engine management wiring is not conveniently in a separate wiring harness which you can just take out and use in another car with minimal modification. The wiring in a Subaru is split up by location in the vehicle, not by function, and this means that to make the Subaru engine run outside of the rest of the Subaru, some work is involved to make an ‘engine management only’ harness from multiple much larger Subaru harnesses.

Price: from £283.33 GBP +VAT (£340)

An MY04 EJ201 Impreza normally aspirated ‘engine management only’ harness made to fit and be 100% ‘plug and play into a T25 / T3 / Vanagon with a VW petrol rev counter
An MY02 EJ201 or EJ251 Legacy normally aspirated EGR ‘engine management only’ harness made to fit and be 100% ‘plug and play into a T25 / T3 / Vanagon
An MY02 EJ201 or EJ251 normally aspirated ‘engine management only’ harness made to fit and be 100% ‘plug and play into a T25 / T3 / Vanagon
Work in progress on an MY02 Impreza turbo harness, in this case for a kit car……

Options – ft ext, fuel pump harness, lambda harness, new VW connectors, bulkhead grommet, immobiliser antenna

harness wrapping spec

Having the engine management wiring work done properly, by someone who knows what they are doing is the one main thing which has the biggest effect on how successfully your Subaru engine will run in your VW. The cost difference between having it done properly and having it done badly is typically not big in the scheme of things (in some cases it will be cheaper to have it done properly – if you do your homework on who to have do the work up front). Why cut corners here? You’ll likely regret it later – we know this as we are where unsatisfied customer of others’ wiring work eventually end up phoning when they finally do their research into who actually understands this stuff well.

We can usually turn harnesses around withing 1 to 6 weeks depending on workload. Typically, it averages around 3 weeks.

Harness work options:

All of our Subaru engine management wiring work options are designed to either make the wiring easier to install into VW’s, or as replacements for VW or Subaru standard parts which are either often missing or were not in all models, but make installation easier.

Front Extension Harness

Price: from £62.50 GBP +VAT (£75)

We developed the front extension harness to extend all of the features which have to be or should be in the front of a rear engined VW from the engine management in the rear when it became apparent that most customers were not happy with extending these to the front themselves.
Front extension harnesses are not a product which can be purchased separately – they are only available at the time we do your engine management wiring work because this includes fitting the necessary connectors for them to plug into. We make front extension harnesses for the following VW models:

  • T25 / T3 / Vanagon
  • Split screen bus
  • Bay window bus
  • Beetle

Depending on the spec of the conversion they extend the following features to the front:

  • Engine check light
  • Immobiliser light
  • Vehicle speed sensor
  • Rev counter signal
  • Radiator fan control
  • Fuel pump
  • Temperature gauge signal

Almost every customer goes for this option – it’s incredibly good value, especially given how expensive the multicore cable they’re made from now is.

New VW Connectors on you Subaru Engine Mangement Harness

Price: £29.17 GBP +VAT (£35)

This option is a set of things which makes the Subaru engine management plug in to the VW connectors in watercooled T25 / T3 / Vanagon models. You’ll probably think the low price is a mistake – it isn’t. More info on that later. It includes:

  • Fitting all the right VW connectors (of the 12 possible combinations) to plug in in your engine compartment junction box.
  • Fitting the correct low coolant level sensor connector to suit your VW and the wiring to it so the low coolant level system works as exactly as VW intended.
  • Wrapping the harness in tape and conduit to OEM specs. This is only viable once the exact routing of the harness in the VW is determined, and for the water cooled models where the engine management plugs in to standard VW connectors, the exact routing isn’t defined until all the relevant VW connectors are fitted. If you don’t go for this option, the harness tape and conduit are supplied loose, for you to fit once you’ve determined the exact routing.
  • Bespoke bulkhead grommet fitted to the harness (fits into a 52 x 90mm slot with full radius ends)
  • Coolant temperature sensor extension cable for conversions using a reversed coolant manifold.

No used parts from your VW wiring needed – we use all new connectors where the wiring plugs into the VW. There are a couple of reasons why this option is so inexpensive. Firstly we source the connectors required much more cheaply than anyone else doing similar work is likely to. Secondly, in our opinion, this option combined with a front extension harness is the right way to install Subaru engine management into the water cooled VW models – plug and play with no modifications to the VW wiring, and we want to encourage all customers to go for it. This works – almost every customer goes for this option.

Only available as an option with our harness work – we don’t sell the individual parts used individually.

Fuel Pump Harness

Price: £10 GBP +VAT (£12)

Late model fuel injected T25 / T3 / Vagagons (1987 –>) had a separate harness for their fuel pumps. This ran from the RH front corner of the engine compartment in 2wd models to the pump, or from the engine compartment junction box to the pump in Syncros. Initially we just stocked the VW connector so we could fit it to the Subaru engine management harnesses and the original VW fuel pump harnesses could plug in, but then realised it made sense to offer a reproduction of those harnesses too as they’re a neat way to withe the pumps in earlier or non injected models which didn’t originally have them.
Fuel pump harnesses are not a product which can be purchased separately – they are only available at the time we do your engine management wiring work because this includes fitting the necessary connectors for them to plug into.
You need to specify whether you are using a ring or a spade terminal fuel pump when ordering.

Rev Counter Interface – built into your wiring harness when we do your harness work

Price £30.00 GBP +VAT (£36.00)

See Rev Counter Interface for more details

Subaru Cruise Control

Price: from £133.33 GBP +VAT (£160)

If your donor car had factory fitted cruise control, it can be used in your VW if you want it. We can only add it at the time we do your engine management wiring work, or if you send the engine management hardware back to us at a later date (so we can install the necessary fuse, wiring and connector). Includes all parts to mount the cruise control hardware.
See Subaru Cruise Control

Lambda / Oxygen / O2 Sensor Extension Harnesses

Price: POA

Through the Subaru engine management harness, the low level lambda / oxygen / O2 wiring uses screened cable to keep out interference from other nearby circuits. Also, the wires on the lambda sensor itself are not copper, so are not easily soldered. Both of these make extending the wiring to the lambda sensor, if required by your exhaust routing, difficult. Also, because the signals are very low level, they are more prone to stray resistance from dodgy connections (such as trying to solder to the non copper wires). The best way to extend the lambda sensor wiring if required is via a plug in ‘extension lead’.
We stock the new connectors to make extension cabled for almost all of the (many) Subaru lambda sensors. These are not ‘off the shelf’ products – they’re made to order for each customer. You have to tell us how long you need the extension cable to be.

Replacement Subaru Lambda / Oxygen / O2 Sensor Adaptor Harnesses

Various Subaru models use short adaptor harnesses between the main engine management harness and the sensor(s). These are sometimes missing when customers buy the parts from a donor car – usually because that car was in a breakers yard, and they’d already removed the catalytic converter(s) to sell them, leaving the sensors and adaptor harness attached to the cats. These are the genuine Subaru parts that our reproductions replace:

  • Wideband and narrowband lambda adaptor
  • Wideband only lambda adaptor

The lambda adaptor harnesses can be custom made to non standard lengths if you would have also needed a lambda extension harness.

Immobiliser Antenna

Price: £50 GBP +VAT (£60)

If you have the MY00 onwards engine with the Mitsubishi immobiliser, but don’t have, or don’t want to use the key and lock barrel assembly in your conversion project, we make a new immobiliser antenna which reads the transponder chip without the key body or ignition lock barrel being present. These are far smaller and neater then using the key and ignition lock barrel, but are not suitable for use when you want to use the immobiliser to immobilise your VW. Originally designed for customers who do not have the key body or ignition lock barrel – just the ECU, immobiliser ECU and transponder chip:

Immobiliser Antenna Assembly
Assembled
Immobiliser Antenna Fitted

Transponder chip and immobiliser ECU not included. Only available as an option with our harness work – not sold individually.

Almost all of the others doing Subaru conversion engine management wiring work, at least here in the UK, base their work very heavily on attempting to copy work done by others. Originally they were typically following the MY90-94 EJ22 wiring diagrams for VW conversions from the US. Back then the US spec models were near identical to European spec, but never after that. This is why some of them typically only fitted EJ22 engines for so many years when other engines were far more widely available (the EJ20’s and EJ25’s from the late ’90’s).

We were the first doing Subaru engine conversion wiring work in the UK to:

  • mount all the non weatherproof hardware inside the VW in the dry (some continued mounting some or all of it in the engine compartment, often in the wettest possible location for many more years – absolute idiocy)
  • gain a thorough understanding of the Mitsubishi immobilisers – enough to make our own antennas for them
  • wire the engine management power supplies correctly and fuse them correctly
  • decipher all 12 of the T25 / T3 / Vanagon engine harness connector combinations and stock all of the relevant connectors so that we can fit them to customers harnesses without using and used VW connectors
  • we take great pride in our wiring work. You’d think that’d be a given, right? If so, have a look at this example of a UK competitors work


Just following someone else’s instructions, where they exist, to convert Subaru wiring for VW use is great if it’s a one off DIY job and you’re not interested in how any of it works. But to try to tun a business on that basis is a dreadful idea, because you start with no knowledge of the systems you’re working on, and never gain that knowledge by doing the work either. This explains a lot of the inexplicably bizarre changes some (mostly one) of them made to the engine management in large numbers of their customers conversions over so many years (see here for the worst examples we’ve seen . You won’t believe how bad many of them are – you’d struggle to guess then or make them up, never mind understand the logic of those who decided they were good things to do). The only way to be able to diagnose problems with the engine management when the inevitably occur is to have a good understanding of how it all works, and by attempting to follow others’ instructions of copy others’ work will never give much understanding


The only way to gain the knowledge to be able to diagnose engine management is to learn as much as possible about it, and the best way to do that is to develop everything about how to modify the harness for VW use yourself, from scratch (i.e. with no influence from how others do similar things – unless you have connections to the engineers who originally developed the exact systems you’re working with). That means learning as much as possible about how the systems work, and experimenting with them. That along with information from text books and OEM documentation )especially Bosch) is where all of our knowledge of Subaru engine management comes from. This is the approach we took, and we pioneered using the engine management on all of the Phase II Subaru engines in the UK.

Another UK competitor until recently was promoting his wiring work to his customers as being a copy of our work (and may still be). We had a few customers wanting to purchase wiring options which we make but they don’t to try to use with their work. That was never likely to be an option, but the interesting thing is that it meant we got out hands on two harnesses which they had sold as being copies of our work to see how viable using our wiring options with it were. What they had copied was laughable. The basic shape, what fuse boxes we’ve always used, what aftermarket connectors we use for certain applications, etc. but that was about it. Little if anything in common with how it works, and no ability to plug in our options without major reworking (even though they’d used the same connector). Multiple errors were found in both of them. Pretty amateur quality, which is not surprising given we’d had a 12-ish year head start by then. Learn your work by copying, and you’ll always be catching up – never ahead. Their work is cheap, and you get what you pay for. They claim to have done an absurdly high number of Subaru harness conversions for VW’s given the time they’ve been doing them for.

Regardless of how good they are, if they have never worked on Subaru engine management before, and you’re paying them by the hour, you’ll be paying far more then you need to. Probably for a less thorough job too. This is for three reasons:
1. Understanding the finer details of what is required to make a stand-alone engine management harness from the Subaru harnesses is not trivial. Even an OEM engine management engineer from a different brand would be unlikely to pick up on all of them for some harness specs the first time they work on one. They’re often not covered in any Subaru documentation.
2. Subaru wiring diagrams are notoriously difficult to definitively match up to wiring harnesses. Unlike VW wiring diagrams, which generally tell you exactly what engine code and model year they cover, no Subaru wiring diagrams show that info. In many ways the Subaru wiring diagrams are better than VW diagrams, bun not in terms of identifying what they cover.
3. Subaru’s wiring colour coding is not consistent. Once you understand Subaru wiring, this is no big deal at all, but to those unfamiliar it causes a lot of confusion, including often overlooking correct wiring diagrams. It also seems to make those only familiar with working on harnesses with consistent colour codes such as VW find working on them unbearable, but there is no need for this – it’s just a different process, not really any better or worse (they both have their advantages and disadvantages).

In most cases, no. How you’re likely to get on with it has more to do with your approach when you get stuck or find something that you weren’t expecting than what you’ve done before in out opinion. If you panic / get annoyed / lose interest, it’s definitely not a job for you. To succeed, it helps an awful lot if you have an interest in engine management. If you’re also patient, and see getting stuck as an opportunity to learn more, etc, your chances of succeeding increase enormously.
Most folk who work on cars either know that are or are not happy working on wiring harnesses, with the majority being in the latter group. That’s fine – it’s definitely not most people’s cup of tea.
Expect to put a lot of time into it if you’re making a stand-alone engine management harness from Subaru harnesses for the first time. As an example the first one we did back in 2003, we put a whole week’s work into it. That was with the interest in engine management up front, past experience of automotive wiring harnesses (wiring a car from scratch, etc), and working on a management system which nobody else has used in VW conversions at that point (MY00 European spec Legacy EJ201).
If you’re thinking of having a go at your wiring work yourself, but are not sure whether it’s your thing, you’re in a minority (most have a clear idea up front), Consider all of the above before you start. If you get out of your depth and end up wanting someone to finish the job for you, expect this to cost more than if they had done the whole job for you, starting with unmodified Subaru harnesses. If they know the job inside out and are willing to put their name to the work which you started, they’ll first have to identify and check every single thing that you have done to the harness (and often re-do some of it), and doing that is time consuming.

If you’re going into it from scratch with no prior experience but an assumption that you’ll be able to do it, don’t be surprised when you get out of your depth. There have been a couple of interesting examples of this documented in great detail on Youtube over the past couple of years. One with two guys with a CAN bus Subaru engine, and one with a guy attempting to put an Audi V8 into a road legal Porsche. All seemed nice folks, just with excess confidence about what they were attempting to work on. It was extremely obvious from the beginning to anyone who works on this stuff professionally that they were not going to achieve what they expected. Both were examples of the Dunning – Kruger effect in action. The excess confidence being due to them having absolutely no idea how far out of their depth they were. Both conversions are not impossible, but require some highly specialist knowledge. One seemingly gave up, and the other went around and around in circles, pouting more and more money into the project, seemingly still without a clear path co completion. Their time would be much better spent learning more about and understanding what they’re doing than making videos.

Sorry, no. Providing Subaru wiring diagrams for folks doing VW conversion wiring work DIY just isn’t practical, for multiple reasons:

  1. We have no copyright to distribute Subaru wiring diagrams.
  2. Matching wiring diagrams to Subaru harnesses is a real black art. After working with Subaru engine management for 20 years, we still frequently start believing a harness is one spec before finding that first guess was wrong, and having to switch to a different ‘diagram’ (we actually don’t use diagrams at all for the most commonly used Subaru engine specs – we use a large table showing all of the relevant information for each variant that we’ve developed, as it speeds the job up).
    Unlike VW wiring diagrams, which generally tell you exactly what engine code and model year they cover, no Subaru wiring diagrams show that info. In many ways the Subaru wiring diagrams are better than VW diagrams, but not in terms of identifying what they cover. Definitively matching up harnesses and diagrams without having the harness in front of you is next to impossible.
  3. Subaru are a very small car manufacturer, yet they use an insane number of different engine management systems each with different diagrams. All manufacturers do, as emissions requirements usually mean each engine management variant rarely last more than about 3 years. Each engine wiring diagram is between 2 and 15 pages long, and we have collected hundreds of them. We have over 50GB of genuine Subaru workshop manuals.
  4. Subaru engine management wiring diagrams do not show everything you need to complete the wiring work for a VW conversion. For example they never show the power supply, radiator fan control, immobiliser, etc. circuits. Those are all covered in separate diagrams. While the right (genuine) service manual always shows every relevant engine management diagram, they frequently only show some of these other diagrams that are needed. This means that you’ll frequently find wiring leaving the engine management diagram with references to what other diagram they re-appear on, only to find that the page you need isn’t there. Or in the case of the transponder key immobiliser or the factory fitted Sigma M30 or S30 immobiliser, frequently non of them are in the manual. Other info is specific to the VW installation, so Subaru clearly don’t show it.

Therefore re-drawing all of the Subaru diagrams to show all the modifications needed to work in all VW models and avoid any copyright issues so we could distribute them legally is not ever going to be remotely close to practical.

No matter what excuses they come up with, there is no circumstance where is is acceptable to have removed any of the diagnostic features from your Subaru engine management. It is almost no effort or extra work to leave them in and functioning correctly. Even if you hide the connectors and lights away and never look at them again, they’re invaluable, free tools which are incredibly useful if you have to diagnose anything. Yet there are large numbers of conversions in the UK with some or all of them removed. All of the diagnostic features were routinely ripped out of all the harnesses done by one company. In their case, the reasons why are obvious. They have almost no understanding of how the electrical systems they modify work, and as such are almost certainly not capable of understanding how to make the diagnostic features work in a VW. Also, other mistakes in their wiring mean their conversions run with many error codes, and they’d rather their customers not know that.

Yes, but……

We like our engine management wiring work to be highly standardised. Ideally we’d always start with unmodified Subaru harnesses, as this make the job totally routine. We don’t really want engine management wiring work which doesn’t follow this. However, there is a steady demand for this kind of work, and we’ve tried various approaches to helping customers in such a situation over the years. Initially we tried just doing the job that the customer requested (typically putting back features which someone else removed), but quickly realised that this couldn’t work in any way that we were happy putting our name to. Harnesses would arrive to say put the diagnostic features back, but they’d have no fuse box, and very frequently we’d find that the power supply was wired totally incorrectly too. Too often we’d end up correcting all of that too, even if the customer didn’t want it, because we didn’t want any association with harnesses with their power supplies wired so badly, at our expense. This wasn’t viable, so for a few years we stopped doing any kind of rework on harnesses that others have previously worked on. But the demand remained.

What we eventually settled on is that we will take on harness rework jobs (as long as what the customer has is not too far gone), either on harnesses done badly by someone else, or uncompleted by DIYers who got out of their depth, but we’ll only do them if we convert the entire harness to as close as is possible to the spec we would have done it to if we’d done the work in the first place. Usually that’s functionally identical, but with extra wire joins which wouldn’t usually be there. This is always more work than us having done the whole job originally, so always costs more. We’re always happy with the end result that way, and we can still help customers who have incomplete or faulty engine management.

The following features are frequently missed out from Subaru engine management systems converted for VW use when done by amateurs, ‘specialists’ who don’t a have a sufficient understanding of the systems they are working on, or ‘specialists’ who prioritise cutting corners to increase profit over doing the job properly:

  • Alternator wiring (leaving you to wire up the alternator yourself)
  • Diagnostic connectors
  • Engine check light
  • Immobiliser LED
  • Cold start circuit
  • Extending all of the relevant wiring to the front of the VW, or offering an option to do this
  • Rev counter interfaces, where required
  • Offering an option to have new VW connectors fitted at every single location where the wiring interfaces with that I the VW, making the wiring 100% ‘plug and play’, without requiring any used VW connectors. 

As long as all or sometimes most of the parts are present, Subaru harnesses are rarely beyond repair. But they are sometimes beyond economical repair. If yours is beyond economical repair, sometimes we’ll be able to help, but not very often.

Matching harnesses to Subaru engine management systems is a real black art. No information on how to do this which helps much is available from Subaru – it comes work to whoever is doing the matching having experience and ideally having kept a lot of information over many years work on Subaru engine management. Definitively proving that a harness is the right one is especially difficult if the potential harness comes without any information about what model it came out of or in particular what ECU part number wen’t with it. This is especially difficult with some of the mid to late 1990’s European spec models, but it isn’t easy with most models.

The reason is that with most of the engine management variants, there are also other variants which are near identical, but not compatible. For instance, some use all the same engine management connectors, in all the same locations, but the wiring between them is different. For this reason we very highry recommend that customers so not attempt to assemble an engine management system from parts which do not come from the same donor car as the engine. If you do do, you’re massively increasing the chances of having big problems.

We usually have a few spare Subaru engine management harnesses. Often these have been bought off customers who don’t need them, etc. The problem is that because there are so many different harness spec, we’ve had some of them for 10 years +, as the chances of a customer who needs a replacement harness needing that particular one are not high.

If we do the wiring work to create the ‘engine management only’ harness for you, and you go for the options we do to make the wiring as simple to install as possible, it’s not really possible to make it any simpler. You don’t really need to know anything about wiring or engine management to be able to install it – only to be able to plug things in (in the case of the water cooled VW models) or plug things in and make 3 connections to the VW wiring (air cooled VW models). You don’t need to know what anything does or is (although that obviously helps). All of the connectors are either unique or uniquely colour coded, so the biggest mistake you can make is not plugging something in. This can prevent the engine from running, or cause error codes, but it can’t cause any damage.

Sorry, no. We never shorten or lengthen Subaru engine management harnesses, for a few reasons. All are long enough to mount all of the non weatherproof hardware inside the VW. The amount of joins you end up with which shouldn’t be there always makes shortening or lengthening the harnesses a mess. The only exception is when we do the Subaru cruise control wiring or ‘drive by wire’ throttle wiring work for you, as in both cases all the joins can be inside (i.e. away from the weather), there are far less of them, and lengthening the Subaru wiring is unavoidable in a rear engined VW with these systems.

Our Subaru engine management wiring work is highly standardised, we do it very much on a basis of minimum joins in wires. Anything which involves drastically deviating from the way we do it such as lengthening or shortening harnesses, and it probably won’t be a job we’re interested in.

Possibly. That depends what is missing or damaged. We have some stock of used Subaru connectors / incomplete harnesses for use in repairs, and also stock a lot of the more commonly needed connectors:

A selection of the new Subaru and VW connectors we stock for use in our wiring work and / or repairs