1G 87 Mighty Max Harness Repair Help

[ItsJustin]

Good afternoon again guys!

I am currently in the process of swapping '90 6-bolt into my '87 Mighty Max, with a somewhat frankensteined 91-94 harness.

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Motor is mounted and sitting happy, but now I'm in the process of trying to reverse engineer whatever the heck one of the previous owners of this harness did. There are so many splices and just straight up cut wires that I've been slowly labeling and repairing or removing depending on if I need them.

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I've gotten the ECU pinouts from the ECMLink website and the wiring schematics from here that I'm using to work through this.

Can anybody tell me what you would possibly want to splice into your O2 sensor and Knock Sensor pins to the ECU? I of course don't know this platform, but I can't think of any reason you'd want that.

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Harness already has GM MAP sensor and IAT sensor provisions spliced in so I assume the last car was running a SD tune if that makes a difference?

Just trying to get an idea before I commit to completely unlooming the whole thing and starting again

Thanks for your time!
-Justin

 

[Djean1G]

Hello I believe the wire cross with the knock sensor to 02 sensor is a hack so there is power to it low but will make the knock sensor read it like it was the knock sensor posaible hack heard it somewhere years back.. good luck you can do it.

 

[steve]

The knock wire and it's related ground and braided shield looks normal going to pin 9.

The O2 sensor wiring going to pin 4 looks hosed. It's ok that the braided shield connects with the knock shield and ground but I don't know why the white wire is connected to those black wires? Is that to the ground connector?

 

[ItsJustin]

Thanks for getting back to me fellas!

Started shooting wires with the multi meter today and it seems like the previous owner has tried to splice as many grounds together as he can, so that’s what was happening with the shields and blacks seemingly tangled with the O2 and Knock sensor, however that random black and red that was spliced in there ended up going nowhere, just an open end far down the harness, I assume that’s where he wired an AFR gauge or something, so I’ve pulled that out and rejoined the O2 wire and it’s a lot less of a concern now.

I do keep finding clusters of electrical tape and cut wires so that is absolutely concerning me, but nothing that will stop me from getting the truck running I hope!

Now I just gotta find a water pipe and the truck should be running in the next few weeks!