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Harness Building

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Site last updated on 15/08/08

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  Making an ‘engine only’ harness from your Subaru harness involves removing all the other circuits such as lighting, wipers, heater, etc to leave just what is needed to run the engine. The entire engine circuit is left as Subaru intended in all harnesses converted bu RJES, so converted harnesses have the following features:

    • All new conduit fitted
    • A new fuse box is fitted, with all fuses sized as Subaru intended
    • All Subaru check mode and diagnostic connectors are retained
    • A new engine check light is fitted (for reading error codes)
    • The Subaru ECU is used to switch the radiator fan rather than a temperature switch (the ECU’s use more than just coolant temperature to determine whether the fan ought to be on)
    • The fuel pump is ECU switched to maintain the factory fitted safety cut off
    • Fitting instructions included, including an explanation of what each wire that you need to connect does. The instructions are customised to suit your specific harness if required.

  We pride ourselves on the standard of our wiring work. The objective is to end up with an near OEM quality wiring harness for youe Subaru conversion. Quality automotive wiring components will be used throughout, with non of the wiring bodges often seen on engine conversions (even on some professionally done ones), such as mismatched wire sizes, pieces of domestic mains wire, so called ‘pre insulated’ single crimp connectors, Scotchlok connectors, terminal block, etc..
  All required Subaru harness features will be retained. Outputs will be modified to interface with the VW instruments if required. Any non required features (typically other circuits which interfaced with the engine ECU in the Subaru) will be insulated and identified in the harness near the ECU, and hidden in the conduit, just in case they should ever be needed.


JDM (or ‘grey import’) Subaru Wiring Harnesses - Important Note: If your harness is from a JDM Subaru (Japanese domestic market - i.e. a grey import), please note that the wiring diagrams for these models were only originally available in Japanese. They are almost always wired differently to European, US and Australian models. Some are quite similar to non Japanese equivalents, but without a diagram it can be difficult or near impossible to finish the wiring conversion work off.
   If you want the wiring work done for a JDM engine, it will cost £20 more than a near equivalent non JDM model IF YOU SUPPLY THE CORRECT WIRING DIAGRAM, IN ENGLISH! or if it’a a model which we have wired before. To know’ ve’ll need your ECU part number (format 12345 AB678). If you don’t supply the correct wiring diagram, or it’s not a spec we’ve done before we may still be able to wire the engine, but be aware that there can very easily be more than two or three times as much work involved, and this will be chargeable per hour. It is not uncommon to spend a day on the internet trying to find a wiring diagram for a JDM Subaru in English, and to find nothing. A JDM harness without the VIN Number of the donor car may decrease the chances of finding any relevant wiring info.
   All our wiring work is done assuming the harness you have supplied is non JDM unless you state otherwise. If you send a JDM harness without realising that it is JDM, it may not be possible to complete the harness work, as it won’t be apparent that it is JDM until half way through the conversion work.
   In order to find out whether your engine / harness / ECU are JDM or not, look at the donor car’s VIN number. If it’s 17 digits, it’s not JDM. If it’s 10 digits, then it is JDM. This certainly seems to work for 1990’s models. Not sure about later ones.


Harness as Removed from the Subaru:



....and as Converted to an RJES Subaru Engine Harness (note - the on in the pic is not the same one as above)


  OEM quality automotive components are used throughout, including matching rating thin wall insulated wire, ‘double crimp’ connectors, new blade fuse box, new conduit, soldered joins between all cut wires:




Wiring Harness Features Check List:

   If you are shopping around considering using another supplier to carry out your wiring harness conversion work, you may want to check that what you will get back includes the following:

  • The engine check light
  • Diagnostic connectors
  • The cold start circuit
  • An output to drive the VW coolant temperature gauge if for a T25
  • ECU controlled radiator fans are nice to have too, as Subaru's use more than just coolant temperature to determine when the fan should be on.

   Don't accept that any of the above 'can't be kept' in a VW conversion, etc as an answer, as this is simply not correct. There are definitely people out there doing harness work in the UK and telling customers this, and the only possible explanation can be that they don't understand enough about how the Subaru circuits work, and have a ‘cut off everything we don’t understand’ attitude. All of the above can be retained in any VW conversion using any Subaru engine, and the first three definitely should be. Without them the job has not been done correctly. All of the above are retained in all harnesses converted by RJES.
   Unfortunately the standard of work on Subaru wiring harnesses for VW's is not all equal, and we have fixed, or helped the owners to fix quite a number of converted VW’s which had some or all of the above features missing....


Harness Conversion Work Cost Calculator

   Filling in the table below will give you a price for converting a Subaru harness based on ot’s specification:

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Note 1:  Please include the engine harness connectors from inside the black engine bay junction box your T25 engine. These must have at least 100mm of wire attached. Also include the low coolant level sensor wire and connector, unless you want to wire it back up yourself, or don't intend to use it.

   To order a harness please copy the completed table into an e-mail (the mail will need to be formatted as html), and send the mail to us:     email_address_image02or print the table off, and include it when you send the harness. If you are unsure about how to copy and paste the table into an e-mail, please click how to paste table into an e-mail. Alternatively you can download the file and open it with Excel, then save and return it by e-mail.





Harness building terms and conditions:
Harness Testing:
  All harness work is done untested, and as such is unwarranted. Where each modified wire is connected to is double checked before dispatch. We don’t know whether a harness / ECU which you supplied worked when it arrived, and don’t have your engine (unless you want to bring it along for a test). However, should you encounter a problem with harness, we will correct it on a ‘return to base’ basis - (i.e you send the harness and or engine / vehicle to us, at your expense, not vice versa) for no charge if the fault proves to be an error on buliding the harness. If a fault proves to be caused by faulty and / or a mismatched set of components supplied by the customer, then any fault finding / repair work will be chargeable at £25 per hour, subject to your approval. Note that you will have incurred some cost by the time such a fault is diagnosed.

Harness Condition:
  The prices quoted for harness work on the ‘prices’ page assume that nothing in the Subaru harness which is critical is cut, damaged, modified or missing. These all at least add extra work, or at worst may render the harness scrap if they can't be repaired / understood. If a harness sent for modification is found to need repair work, then this will be charged at an additional £25 per hour, subject to your approval.

Wire Colour Codes:
  Although a circuit diagram for a Subaru may be identical to the actual circuit, there is no guerantee that all wire colours will match. Most will, but mismatches are common, often because the diagram is for a car sold into a different market, etc. For this reason, Subaru colour codes in general can not be relied upon unless you know you have an exact match between the car and the diagram. We don’t use colour codes at all when working on Subaru harnesses, so can’t tell you what a certain coloured wire does, or what colour a certain wire should be. Because of the very high number of wire colour combinations used in Subaru’s it is neither practical nor possible for us to keep all of them in stock. For this reason, where wires have had to be extended, etc, a wire of the same rating with any colour will have been used.

 Inventors of the Subaru - VW conversion bell housing using Subaru flywheel, clutch and starter

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