Wiring Harness

Tonight I started working on the engine wiring harness.  Doing an engine swap requires some sort of engine harness to be used along with the computer (ECM) in order to make the engine work.  This is the part where “old school” hot-rodders shudder and panic about.  This is also the part the trips up many folks attempting to run electronic fuel injection (EFI).

I’ve worked with my cousin Jim for the past 15 years perfecting the fine art of transforming a stock wiring harness into something that can be used to fully run a modern EFI engine in a classic car.  At first we worked on “throttle body” engines – basically a glorified carburetor but with the advantage of electronics.  These were the early EFI setups that offered much better economy than a plain carburetor but had a long way to go.  Throttle bodies evolved into individual injectors feeding each cylinder and more sophisticated ECM’s.

Through the years, we were able to adapt the L98 Tuned Port v8 with it’s distinctive intake with eight runners going to each cylinder.  As the L98’s became scarce we moved to LT1’s and LT4’s.  During this time, we also mastered the L32 V6 as originally fitted to bowtie6.  The next step was the LSx family of engines.  Currently we’ve focused on the ECOTEC engine as fitted in Jim’s TR4 and now my TR6.

The throttle body harnesses were the simplest.  No much really to figure out.  When we started using L98’s and LTx’s in Jaguar XJ6 and XJS conversions, at first we sourced the harnesses.  They were not cheap, so we took a stab at using original GM harnesses and cleaning them up.  If done properly they make an excellent harness however it takes some effort to figure them out.

This photo shows the harness from a wrecked 2.4 ECOTEC powered HHR.  The harness is basically all there; however it must be modified to work with the ECM and placement in the engine fitted to bowtie6.  This photo shows the harness after I had removed all the plastic casings protecting the harness.  This is done for several reason, among them exposing all circuits and it is easier to trace the wires to decide what needs removal.

We don’t use the original GM fusebox.  We also remove redundant ground wires and hot feeds, thus allowing the harness to be much simpler and easier to deal with.  Depending on what donor harness you use, certain pinouts on the ECM connectors must be relocated.  This is all done by using original GM Factory Service Manuals.

I’ll have more as the process takes shape.  This is actually a lot of fun however it is a little time consuming.  At the end of the day, it is a very rewarding feeling when the harness allows the engine to run.

4 thoughts on “Wiring Harness

  1. Dick Olds

    I sure don’t want to use the BCM. I’ve never delved into ECM tuning before. Do you think I would be successful in using HP Tuner etc. to clear all of the unused stuff (VAT, evap cannister, BCM stuff, etc.), or should I just send it off to a 3rd party and pray it works? I haven’t found anyone in the St. Louis area that is up on this stuff. Also, I chose the auto trans because it seemed the Aisin 5-speed shift lever would be way too far back from a TR firewall and interfere with the e-brake handle. With your engine sitting so far aft, isn’t that a problem?
    Thanks again for the superb website.

    1. bowtie6 Post author

      The AR5 needs to be modified to be made shorter so the shifter sits in the proper place. Or you can move the handbrake mechanism a bit rearward – my case we’ve done both. You will need to make a new tranny cover, including the section where the handbrake handle is attached to. My car has a two piece tunnel and this allowed us to place everything in the right place. All this though is the least of your worries… There will be significant changes in order to make a proper transmission mount.

      I’ve used HP Tuners to take out the VATS. I have not seen anything that “clears” the BCM. I don’t use one and have no issues. The ECM will require basic tuning. For example, the stock plastic intake is not going to fit in the engine bay (the steering column is in the way), that is why we run a custom made intake. Ditto for the exhaust manifold. Changing the intake though will require recalibrating the MAF since the intake plumbing will be different. After a bit of tuning, I have finally been able to get it close But it is not dead-nuts. All I can say is that this particular aspect takes a great deal of reading, research and more reading.

      While on the subject, you will need to source the appropriate ECM (ie., the proper year model, OS version, etc). There is a difference between the automatic vs the A5 versions and from what I have found, they are not interchangeable. You will also need to get the proper throttle pedal to make the “fly-by-wire” butterfly work.

  2. Dick Olds

    I am ecstatic to see a Triumph/ecotec project. That is exactly what I am doing – putting a ’07 HHR LE5/ECM/harness and Sky 5L40E auto transmission, TCM, and shifter into a ’66 TR4A. I’m hoping to see how you handle all sorts of interfaces, including the wiring harness.

    1. bowtie6 Post author

      Well, we’ve done a 1964 TR4 that my cousin owns. His has the same basic setup mine does, however he made an aluminium bonnet and boot lid. This saves a huge amount of weight.

      Regarding your question about the wiring harness: we started with the stock GM harness which was modified and simplified to fit our requirements. We had to lengthen several wires to make things look nice and neat. The reminder of our wiring was all hand made, once again to fit our needs. Instrumentation is all new electronic VDO Vision series. All sensors and sending units are GM, except for the fuel sender which is VDO.

      Yes, there were several “headaches” we had to deal with. You have quite a challenge there making the ECM work along with the TCM for the tranny since you are running the auto. Are you planning to run the BCM?


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