fwd harness in rwd car

[Mr_Efficiency]

I have an 88 S10 with a 2.5 in it. The plan is to swap in a 2.8 hybrid and run it off a 90 Grand Prix harness.

I'm in the process of striping the Grand Prix of the harness and I've run into some issues. Originally i thought everything engine bay side would be for the engine and only a few wires that i need would go into the firewall for the key (Main power, starting etc...) but I found a huge bundle of wires going into the firewall and i'm afriad to cut any of them.
I have been following them one by one and labeling them as i cut and so far other than the 4 or 5 thick main power ones the rest seem rather useless. A lot of them are for lights and things, but why are the wires for the lights running into the ecm?

Baiscally I just need to know bare minimum what i need to run the motor, for the lights and other acessories I'm leaving that part alone on the s10.

I was hoping the Grand Prix would be just like the cavaliers and such. they are simple, strip everything in the engine bay and the foot long harness that goes through the firewall to the ecm and your done... the GP is a lot more complex.

Anyways, anyone done anything similar who can help out? or even someone to give me some ideas as to what to look for?
thanks

[Superdave]

the GP must have the dash harness all in one deal...

yah, the Jbody harness would work better. might save alot of trouble just to find one.

[Mr_Efficiency]

So i need the entire under dash stuff to? thats seems kinda dumb, there is no way to get around that?

I already cut tons of stuff under the dash, lol but it was speaker stuff and lights and A/C junk. I dont understand why the car needs that to run?

Not saying your wrong, im just curious as to why its set up that way.

[Superdave]

So i need the entire under dash stuff to? thats seems kinda dumb, there is no way to get around that?

I already cut tons of stuff under the dash, lol but it was speaker stuff and lights and A/C junk. I dont understand why the car needs that to run?

Not saying your wrong, im just curious as to why its set up that way.

It just seems like the GP is a mess when the Jbody one works better.

in a J body all the engine controll stuff runs into 1 harness that goes into the cowl on the passenger side, it's as simple as that. All the Jbody dash stuff and other junk either goes through the cowl on the drivers side or it plugs into the ECM under the dash (gauge outputs like the speedo and warning lights).


no, you don't need any of the extra junk to make it run.. just all the ECM's wires.

[Mr_Efficiency]

Yeah, i have had a j body apart a million times, was just that i happen to have a GP here right now.

Guess I'll just run a J body harness, a lot less hassle.

So basically all i have to do with the J body harness is find and wire up the wires for the main power to the ecm and the key so it will start and thats it?

Anyone have or know where I can find the pin outs for the J body harness at the firewall on the drivers side?
I have basic schematics but it dosent show pin #'s

Edit: Does anyone know if the S10 used a spedo cable in 88 or was it electronic?

[Superdave]

here are the diagrams...

http://www.v6z24.com/jbodyforum/ecm-pin-out-diagrams-t99212.html

not sure about the speedo...

[Mr_Efficiency]

Awesome thanks, how do i know what pin is which on the plug? are they labeled underneath the pin? I noticed the GP is like that.

[Scott_68B]

FYI, I took the entire engine bay harness out of a 91 Lumina including both the right and left side fuse boxes...cut the wires off at the firewall. This model has the 7727 ECM under the hood. I spliced it into the wiring harness on my MGB without an issue. The original MG harness is still there for all lights and the gauges, etc. Basically, I cut all the wires I wasn't going to use off of the harness and then supplied power to the fuse boxes and ECM and cut and spliced everything to fit into the MG engine compartment.

-- Scott

[Mr_Efficiency]

Actually i'm looking at the GP harness and other than the large red, orange, yellow and pink thick ones there is just 15 wires that go to the dash and I think they are all for the cluster, I'm looking at my GP wiring diagrams now trying to find out where they all go. If i can find that out then im good to go.

Edit: I'd rather use a GP harness just cause if I decide to go turbo i just have to swap in a TGP chip and a 2 bar map and i'm good to go.

Also what all did you have to wire up from the conector that goes into the firewall? can i get away with just putting power to all the power wires and then ignore the other 15? I only have one fuse box that was mounted next to the ECM, where is the other one your talking about?

[Scott_68B]

I didn't use any of the wires going into firewall...everything I needed was in the under the hood wiring harness. One of the fuse boxes contains the fuel pump relay and the main fuse for the ECM. The other has the fuses for the injectors and a few other components plus the relays for the cooling fans. I put power to all the power wires...some are hot all the time, others are hot only with the key on. You really should get a wiring diagram for both vehicles and study them for a while. Then draw out a plan for merging the wiring into your S-10. That's what I did...it really wasn't that difficult if you prepare for it.

-- Scott

[Mr_Efficiency]

ah ok I know the second fuse box your talking about now, i didnt really consider it a fuse box as it is just a single relay and a power post.
thanks