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ECM wiring routing

Old 03-16-2019, 04:36 PM
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Join Date: May 2015
Location: Kent, UK
Posts: 234
Car: '85 IROC-Z
Engine: 305cid
Transmission: 5-speed
ECM wiring routing


Just a quick question. I've problems with ECM wiring (code 15...) and I think I've traced it to a break somewhere in the wire where the loom plugs into the ECM under the dash. However, I need to pull that part of the loom out so I can inspect it and work on it. I was hoping I'd be able to disconnect it from the ECM and then pull the wires though into the engine bay to work on them without unplugging everything in the engine bay, but I've read this isn't possible - the 'passthrough' connector won't make it into the engine bay.

Is there another way I can access this wiring? Will it pull through into the wheel well, or is my only option to disconnect the entire harness from the engine and pull it through into the passenger compartment? I'd prefer not to do this as it looks rather complicated, and will be fiddly with the risk of breaking connectors etc...

Many thanks for any advice!

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Old 03-19-2019, 10:52 PM
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Car: 1984 Camaro Berlinetta
Engine: LT1
Transmission: T56 6-speed
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Re: ECM wiring routing

If you pull the connectors from the ECM, disconnect the ECM harness from the dash harness, remove the clip holding the 'pass thru' block,...... you CAN pull that end of the harness all the way back into the engine bay. You've got to "snake" it thru the body and into the fender-well, then pull it thru a hole at the top of the engine bay frame rail. ( There is a wire-loom clip inside the fender-well opening to hold the harness in place at the top of the fender well. ) This last bit of pulling the harness out is tricky; the pass-thru plug has to be turned / moved into the correct position before it can be pulled thru the body-metal gap and finally into the engine bay. You might have to make a few attempts,... spinning the plug in different directions and then re-trying - before it can be wedged thru the gap,......... but it WILL fit thru.

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Old 03-20-2019, 08:52 AM
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Re: ECM wiring routing

Yep...there's a "horseshoe" shaped clip on the inside, that secures the pass-through via a groove on 3 sides of it. With it removed, that whole block stays with the harness, and goes out through the fender-well. There are a few photos of mine coming out in the link below.

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Old 03-20-2019, 09:18 AM
Thread Starter
Join Date: May 2015
Location: Kent, UK
Posts: 234
Car: '85 IROC-Z
Engine: 305cid
Transmission: 5-speed
Re: ECM wiring routing

Thanks guy for the pointers and the photographs - that'll all make it much easier to do now I know what to expect.

It looks like I'll have to jack up the car, get the wheel off and take out the arch liner, but that'll still make it much easier to work on the wiring than trying to solder upside down in the footwell!

I'll try to remember to tell you how I get on, when I finally find the time to do it!


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