TBI harness swap

[Shilaeli hugger]

Well my harnesses are all a nightmare. I scored a taillight harness and tbi engine harness for 20 bucks today. My main concern is the engine harness is from a 1990 k5 and my truck is 87 v20. Any big concerns or problems? It was only harness in area that i could find. I can repin and wire if i have too.

 

[1987 GMC Jimmy]

Well my harnesses are all a nightmare. I scored a taillight harness and tbi engine harness for 20 bucks today. My main concern is the engine harness is from a 1990 k5 and my truck is 87 v20. Any big concerns or problems? It was only harness in area that i could find. I can repin and wire if i have too.

If you happen to be running a 700R4 (I hope not with that big ole truck) or a TH350, your torque converter lock up will match up on the harness. If you have a TH400, you'll have a square, three pin connector dangling, and it'll probably trip the TCC code. If I'm not mistaken, the '90 would have used a different ECM speed input method than previous years. It should work fine, regardless. Not 100% sure on this one, but I'm guessing (unless you plan to put a late, electronic cluster and DRAC module in it) you'll just have to find the pinout for the VSS buffer at the back of the cluster and the 7747 ECM pinout and appropriately bridge those two guys together per your diagrams. It'll only be one wire, and you can bring the speed wire from your harness to the back of the cluster and avoid messing with the ECM connector. All the sensors will match up.

 

[Shilaeli hugger]

If you happen to be running a 700R4 (I hope not with that big ole truck) or a TH350, your torque converter lock up will match up on the harness. If you have a TH400, you'll have a square, three pin connector dangling, and it'll probably trip the TCC code. If I'm not mistaken, the '90 would have used a different ECM speed input method than previous years. It should work fine, regardless. Not 100% sure on this one, but I'm guessing (unless you plan to put a late, electronic cluster and DRAC module in it) you'll just have to find the pinout for the VSS buffer at the back of the cluster and the 7747 ECM pinout and appropriately bridge those two guys together per your diagrams. It'll only be one wire, and you can bring the speed wire from your harness to the back of the cluster and avoid messing with the ECM connector. All the sensors will match up.

Well i do have the th400. Got my harness out today in just a few min (damn i love these trucks). Only thing i can see different is one plug for the ecm. Mine has one plug with 8 wires and new harness has 10. I may just pull it apart n repin it to fit my old plug. All but 2 wires match but plug wont match. Gonna get some wiring print outs just to make sure i do it right.

O yeah the k5 had a speedo cable so no speedo wire to worry bout. There is a single tan (i think) wire on drivers side.of my th400. Whats that for?

 

[Shilaeli hugger]

Well that wont work. K5 harness only has wiring for one relay and body plug is different. Trashin both n on hunt for 87 v20 harness again.

 

[bucket]

Don't trash any harness that is in good shape. People pay money for those

 

[CorvairGeek]

Downshift solonoid

 

[Shilaeli hugger]

Well after seeing what was missing on mine and reading the wiring diagrams... im using mine and adding what i need

Mainly the alternator wiring. They cut it off annd had the plug run to a switch on the dash and alt wasnt hooked to battery. We found the brown wire from body plug and yes it was cut n tucked away like a miatake.

Now from what ive seen on the diagrams the red wire from the alt plug is spliced to a wire running to starter and the battery wire goes to the junction box on firewall (and batery obviously). Am i right on yhis? Dont wanna start cuttin **** without lil reassurance.

 

[bucket]

I like to run the red wire from the Alt plug and put it right to the charge wire stud on the Alt.

 

[Shilaeli hugger]

I like to run the red wire from the Alt plug and put it right to the charge wire stud on the Alt.

Wont that drain the battery?

Also what are both the relays for? I know inea for trans kick down but not sure on other. It has a red wire with plug hangin out.

 

[Shilaeli hugger]

Ok i figured out the alt. Checked moms 86 n the wire is constant hot on her alt so i just ran it to junction block