91 engine harness into my 90

[BrokenTsi]

Im replacing my 90 engine harness. The wires are all brittle, been spliced multiple times, repaired, basically its all hacked up and I have a 92 engine harness at my disposal.

I am just double checking to make sure I got everything I need.

I am using a 90 eprom. I can take care of this by switching pins 6 and 14.

I am using a Q45 tb with the nissan TPS. Easy fix, although the 90 is more convenient, but thats ok.

I have a 92 CAS. Plug and play, done.

I have a 92 coil pack, no problem here.

I guess my question is will I need to switch out the gauge cluster? I don't see why I would need to really.

Other than that, the harness should work just fine, right?

 

[Redwidow]

Looks like you have all the bases covered. The gauge cluster wont change. Sounds like you have it under control

 

[BrokenTsi]

Thats what I thought. Thanks, off to the garage I go.

 

[BrokenTsi]

I came across only one problem.

Inside the car, there is a 16pin connector with 16 wires on whats left of my engine harness from the 90. The 93 engine harness I am using has an 18 pin connector with only 16 wires. Easy enough, I pulled out all the wires and replaced the 18 pin connector with the 16 pin connector and made sure they all corresponded to the 90 harness inside the car.

The only problem is, all the wires match up, color for color........except for one. There is a blue with green stripe on the 90 harness, and on the other side of the connector, there is a solid blue on the 93 engine harness.

Im trying to read all the wiring diagrams to figure out what the wire does, and I can't seem to find it. Any ideas?

 

[Redwidow]

To switch from a 90 ECu to a 91 you have to switch oins 6 and 14 so i would assume that to switch a harness from a 91+ to 1 90 ECu you would have to do the same thing

 

[We're on Boost]

I came across only one problem.

Inside the car, there is a 16pin connector with 16 wires on whats left of my engine harness from the 90. The 93 engine harness I am using has an 18 pin connector with only 16 wires. Easy enough, I pulled out all the wires and replaced the 18 pin connector with the 16 pin connector and made sure they all corresponded to the 90 harness inside the car.

The only problem is, all the wires match up, color for color........except for one. There is a blue with green stripe on the 90 harness, and on the other side of the connector, there is a solid blue on the 93 engine harness.

Im trying to read all the wiring diagrams to figure out what the wire does, and I can't seem to find it. Any ideas?

Well, sounds like you are looking at positions 51 thru 68 on the ecu. On my diagram I see 3 blue wires in that group. One goes to the ISC. The other 2 go to the MFI relay (to a coil in the MFI relay). Seems like we could figure this out if you had the 2 diagrams I'm looking at. One diag shows what all the ecu wires go to, what their colors are, and what position number they are. The other one shows how the positions are numbered on the ecu, so you could tell what positions are opposite each other in the plug. I could scan these diags and post them if you want, maybe they are different than what you have.

The 90 and 93 harnesses might have come from cars w/o air conditioning? That might explain one of the missing wires - position 65 went to a/c. But I see wires at all 18 positions on this diagram I'm looking at. I'll see if I can find the old plug that was in my 90.

 

[BrokenTsi]

Ok, in the service manual, the connector is called "C-58".

This connector isnt for the ECU. its over right above the theft control unit on the passenger side.

Ya know what? I havent checked the original 90 ecu to see if its a blue wire just like the 93. Ill go do that today.

 

[We're on Boost]

Oh!

 

[BrokenTsi]

Well, I solved that problem. Now I found a new problem.

I connected my ECU and there is an extra connector that hooks to the rest of my harness on my 90. The connectors are not the same. The 93 harness has 10 wires, the 90 harness has 7. I believe this is some type of body control harness for interior stuff (hvac, radio, etc...). This connector off the 93 engine harness is located next to the 3 connectors for the ECU.

Any ideas?

I thought the swap to a 91-94 engine harness on a 90 was a simple plug and play install with a few swap of some parts.......

Apparently, its not.

 

[akira235]

i put a 91+ harness in my 90 car, everything was plug and play except for the pins that needed to be switched. I have no idea why you have connectors that don't match up, take a few pictures and maybe i can help

 

[SBstar]

The connector you are having a problem with, just match the colored wires, there will be wires that are not used, that's ok the car will run. I also have a 91+ wiring harness in my 90.

Also for future reference you can trim the connector over on the passenger side and it will clip in.

 

[BrokenTsi]

Ok, thats what I just got done doing.

The 3 extra wires are Green, Green/White, and Black for ground.

I chased the Green wires to pin 6 and 19 on the Ecu, and also the Maf harness (I forget which pins they were)


Pin 6 and 14 are switched for my 90 ecu.


They are for Mass Airflow reset, and idle closed position switch.

I have a Q45 throttle body with NO idle position switch, and I'm only using a GM maf temporarily until I switch over to Speed Density. I left those 3 wires in the original connector so they don't ground out on anything, so I suppose I'm all set if you're saying the car will run...............but will it run ok?

 

[SBstar]

My car runs great...they do not seem to affect anything. Even when I was on the stock ecu (have link now) things ran fine.

Your tachometer will probably not work, you will probably need to swap in a 91+ tachometer into your gauge cluster.

 

[BrokenTsi]

I'm pretty positive it will work. Thanks for the info, I kinda figured it out while I was in the garage, but your post gave me some reassurance as to what I did.

As I was looking at it, and I figured out what those 3 remaining wires were for, I came to the conclusion that they werent really needed. I had all the wires I needed, and I didnt really see what I could possibly use them for.

They appear to be outputs from the ecu, but for what? I can't think of anything.

I dont know if it worked yet, I havent started the car up yet. Its been 2 years since the last time it ran, and I'm just finishing up a huge build that I ended up doing WAY more than I planned.

i put a 91+ harness in my 90 car, everything was plug and play except for the pins that needed to be switched. I have no idea why you have connectors that don't match up, take a few pictures and maybe i can help

I can't explain that. Maybe there is a 2 different harnesses for a 90? An early and late production perhaps??

 

[BrokenTsi]

Ok, in the service manual, the connector is called "C-58".

This connector isnt for the ECU. its over right above the theft control unit on the passenger side.

Ya know what? I havent checked the original 90 body harness to see if its a blue wire just like the 93 body harness. Ill go do that today.

EDITED

I happened to have the whole parts car the engine harness came out of, and from what I remember, that blue wire goes with the blue/green. So....the 90 and 93 body harness has a blue/green wire and the matching wire is blue on the engine harness. Weird, but its correct.

Car runs great.

also, I did have to change to a 91 gauge cluster.