Well i'm well into my engine swap, and as of a few days ago I learned that It isn't necessary to change out the entire wireing harness like I thought. aparently I only need a few parts like the ones that run to the ECU and etc.

Could someone explain what I have to do here? the dash is allready allmost completely apart. So thats not a problem. I'm just confused on how you "merge" the two harnesses.

 

You're keeping the stock ECU and EFI?

I suggest you start by looking at both factory manuals and start drawing yourself a diagram on how to re-pin the engine Wire harness.

 

You have wiring diagrams, right? Decide what stays and what goes, then cut and splice as necessary.

If you want a mmore specific explanation then you'll have to tell the people what ECU you are using and what things you need to keep and what can go.



EDIT: Directfreak beat me to it.

 

This should help some.

Paul's site.

 

actually, pauls site is what put the idea of doing this in my head. I was just going to put in the whole 89 wireing harness in my car, and this seemed much simpiler.

but an explaination of my intended setup should help. I'm putting in the 89 motor in, with the stock fuel injection system. I have every bolton for the motor and the plan is to use them all ans use as little from the 12a as possible. I am also using the stock 89 ecu.
For my exaust I have an GSL-SE exaust manifold, that I will use to cennect the motor to my stock exaust system. I plan on chaging this to a racing beat setup after I pass emissions. I'm looking at using a GSL-SE fuel pump as well.

There is a little bit of stuff on the 86-88 harnes, but about nothing on the 89 harness. I picked up the factory workshop manual for 1989 to help me out on this.

So what kind of advice, tips, walkthrough, etc could you guys help me out with this wireing mess?

 

I would use an aftermaket fuel computer, and a 12A distributor. Using the stock ECU is going to be a nightmare. Especially the 89's with their electronic OMP and 6-port actuators.

Go aftermarket, so when you want to go Turbo in the future (and you will) you won't have much to do.

 

well it really boils down to this, I'm a high school student, therefore I have very little money to spend on this as I have a part time job. So cant afford to go out an buy an aftermarket ECU.

I've allmost completely used up my budget on this, and the motor is ready to go, so I need to make do with what I have. The car is allready torn apart anyway. I also have a time frame to get this done in, not anything specifically it just cant stay in my auto shop class forever.

So given my circumstances what would you guys do? What course of action would you take? Should I go with my origional plan and just use the complete 89 wireing harness?

 

Go ahead. It's gonna take a little while to figure out, but if that's all you got, then make do.

Make some money - document the pin layout for a swap.

 

thanks directfreak. You have been really helpful on this. I really appreciate it. A couple of questions that I havent seen answered anywhere on this forum, I thought you might have the answer to.

1. If I use the 89 harness should everything on the interior work correctly?

Will anything not work, or not work right after this? (I'm guessing yes and yes to that one, but I might be wrong)

2. Will I have to fabricate any connectors or connections?

Answers to any of these questions would help alot

 

Thanks, I'll try.

If it is anything like my GSL-SE, the Engine ECU wiring harness has absolutely nothing to do with the rest of the car - not even the gauge sensors and senders.

On my SE, the wiring harness from the passenger side went to the engine, and came out together in one piece.

Technically, everything should work. Although the 89 plugs control more than the FB one, so you will likely need to add power and or bridge alot of connectors that normally don't have inputs on the FB, but did on the FC. - Ignition, OMP, 6-port actuators, to name a few.

If you have access to the Donor car, then no. You "should" be able to get both sides of the plugs. The engine side and ECU side. The only real concern is what I mentioned previously. The 89+ have electrical OMP's, that get an input from the ECU. If it isn't working properly, the computer goes into "limp home" mode which is basically like 3000 RPM or less. As I stated before, you might just want to bridge those connections, so they think they are running fine, and just use a mechanical OMP or pre-mix. It is harder to use an 89+ ECU, over the 88 or older ones because of these little subtle changes that can wreak havoc on someone trying to figure it out.

Good Luck. When you get crazy and feel like kicking it in the ***, take a break and come back the next day with fresh eyes.

Also, Not to persuade you any differently, but have you checked the MEGASQUIRT Fuel injection computers? That might be a whole lot easier for only a hundred bucks or so, rather than to splice a carbed engine harness to a high-tech EFI one. If you do a search in the 1st gen section, it was covered recently.

 

*DOH* OMG i feel like such a noob here. I didnt even realize that there were two seprate harnesses.

I just went to go check and sure enough they are seprate.

So... do the harnesses connect to eachother?

Can I just leave the BIG harness (the 85 stock one) in, and then use the 89 engine one? Or am I missing somthing big here? (probably)

Also as far as the OMP. I have the 89 one, but I am using a 12a front cover so the engine can mount correctly. (I allready have the mazdatrix 12a to 13b mount) Can I still use the OMP from the 89, or should I use the mechanical method?

 

I would remove everything 12A, then put the 13B with everything in, then route the 13B ECU and plug into place.

Then - Rewire everything in one place only where the ECU goes, under the passanger's feet.

The 12A car doesn't really have an ECU..

 

didnt really think that carbed cars used much of an ECU anyway.

it still cracks me up when I pulled out the ECU to see that there was a big mitsubishi logo on it....

 

Yeah, I'm with directfreak on this, unplug the 12A engine harness and pull it out. Then plug the 89 ECU into the 89 engine harness. Push harness through firewall and plug into motor. Then consult either a wiring diagram or the second gen forum to find out how to do things like plug in +12V and bypassing the OMP controls.

 

just curious, i'm sure the two harnesses link together at some point, so where and how do they connect to eachother?