1991 Z28, 305 auto. Bought and never ran engine. Took the car completely apart and now putting it back together. The car will get an L98 tpi/T56, I already have.

Original engine wire harness is trash and I have a new oem harness that is supposed to be for a 1991 Z28 with a manual transmission that I would like to use. I put the harnesses side by side and there are a few differences.

Please take a look and see if these differences will cause me problems. @Pocket Thank you.

 

 

 

 

 

 

I’ve found.

Tan/blk - Upshift indicator for manual
brown - vss output
orange / black - park/neutral input

 

Backup lights will be the biggest difference

Grab a meter to test those other wires. It looks like that harness needs a little help before going back in

Upshift indicator will not be present for the auto. I don't think it's present for the dash harness at all for autos. Regardless, it's annoying and uneccessary

VSS wires will not change for any 90-92 V6 or TPI car. The VSS goes strait to the ECM. ECM returns 2,000ppm to cruise and 4,000ppm signal to the cluster. Same for auto and T5's
T56 will have an 11ppr or 17ppr VSS signal which requires an adapter module like any T56 swap

P/neutral is not used for any manals

 

Thank you Pocket, my concern is this “clear cluster” (what is it called?) that has the black/wire in place of the orange wire. Orange wires are usually 12v from what little I know.

 

That's the C207 connector

After mulling on it overnight, I think you either have an older TPI harness or TBI base that's been modified (likely older too)

The brown speedo wire is not correct for 90-92 SD TPI, nor the blk/wh on C207 Pin M. That's cluster/buffer box ground for 89 and older cars, where 90-92 have an orange wire there for the hood lamp (12v positive)

Do both new/old harnesses have three ECM connectors? That's an easy tell as the 90-92 730 boxes used three, where older 165 boxes used two

 

Both have the green or sometimes yellow 3rd plug . It is for the 1227730 ecm.
to use the t56 you need to wire in a Dakota digital sgi-100bt.

 

Here they go.

 

Do I not need to worry about these wires or can I use it and just not connect the hood light?

should I “de-pin” the black/white wire from there so it doesn’t ground anything else that would be getting 12v from it?

aside from this, I’ve gone wire to wire and the rest looks the same except for the power connector for battery/starter that my old harness doesn’t have. The old one just has it connected wire to wire.

Thank you for your help guys.