Need wiring help! Any diagrams available?

[zx4133]

Hey guys, Michael here, proud owner of a 1986 Mercury Grand Marquis 5.0L which I'm currently restoring/engine swapping. I'm new to the site but you guys seem really knowledgeable and helpful, so here I am in hopes that you can assist me.

As I mentioned, I'm in the process of restoring a beautiful 1986 Grand Marquis. The thing is... the engine I just put into it is out of a 1991 Grand Marquis. So I'm going to have to do some rewiring. Both were 5.0's from the factory and both are stock, no custom hacky wiring, thank God. When I got the 86, it was just a body, no engine or tranny. I had access to a wrecked 91 with a good low mileage engine and tranny, so that's the back story. Also, I've been a mechanic for about 15 years, so I'm not new to any of this... BUT... the wiring is giving me headaches because a lot of it doesn't match up AND I didn't have the original engine and wiring to look at and reference. It was all cut out (just after the computer) when I got it.

I do have the 91 and all of its wiring, including the stock 91 computer, but as I said, it's different from the 86. About half of the wiring I got figured out but I really need diagrams for the rest. First, do you guys have any advice/tips for a project like this? Am I going to run into any major problems that you know of, or are there any complications or surprises awaiting me? Second, does anyone have a PDF of the engine and chassis wiring diagrams for both the 86 and the 91? They would be super helpful. I'm trying to avoid dropping $50 for 2 manuals just to peek at the wiring. Any help with those diagrams, or just general advice, would be GREATLY appreciated.

Thanks in advance guys.

[zx4133]

Oh I should mention that I tried the free wiring diagrams from Autozone.com and they were not very accurate so they didn't help much. Plus they just show individual wires and not actual harnesses, plugs, connectors, etc.

I also searched google pretty good and didn't find much at all.

[sly]

I'd just swap in the inner fenders from the 91 along with everything that mounts to it and use all the wiring from the 91 as much as I could under the hood. This would help eliminate any issues between the computer and the engine. Getting the rest of the stuff from the dash for controls (HVAC, Lights, etc) would just be a matter of pulling enough off the 91 to match up to the 86 to get it working.the major difference is that the cruise is seperate in the 86 and integrated in the 91's ECM. So you have to option of using either (aka extra wires). If you have a list of wires that are loose from the ECM or connectors that are loose and pics of them, we can probably figure out what's needed and what's not. I have a Chiltons for the basic diagrams, but they are lacking for some of the hackery required for swaps like this.Pulling the cluster and HVAC controls to get access to harnesses for ringing out wires to the engine bay will help loads.

[sly]

also, depending on where you're located... help might actually be near in the form of another set of hands.

[85crownHPP]

Ugh, this could be even more frustrating than it should be (as far as making everything plug in nice and look factory), since you have an '86 car. 86 was the first SEFI year for boxes and has all kinds of 1986 only bits, surely including wiring.

If it comes down to it, you can Frankenstein some wiring and make it run.

Get the Transmission/O2 sensor wiring out of the 91 too, if you didn't, and keep the 91's ECM harness 100% complete, using its power supply connection at the solenoid and it's relays. Don't forget the little black wire that goes right to battery ground, that's for the ECM. You might need new o2 sensors, due to the 86 thing...

I'm guessing the bulk of your troubles are hooking the ECM harness into the body harness at the driver's fender, and some wiring near the heater box?
If you still have enough of the 86's engine-side wiring there, nip off the connectors leaving pigtails to use (with one from the 91's body-end wiring) to make a plug-n-play jumper harness (if you didn't). Same with the wiring at the heater box.
If you're lucky, most (if not all) of the wire colors may match up, but surely there will be some missing / some extra to figure out. I'll try to take some snapshots on my 91's EVTM at those connectors, but don't hold your breath for it. And actually if you check out some of the CFI to SEFI conversion threads, most of the important wires get ID'ed with some explanation of how they tie in.

[gadget73]

you'll end up with extra wires on both sides I expect, probably most of them on the 91 harness side. It has inputs and outputs for the cruise control, which are not used on the 86. If you can ID those, that should make this somewhat easier. Unfortunately I don't have either of the diagrams in front of me. I have an 86 Towncar and a 91 Mark VII book, but there are probably enough differences there to screw you up.

[pantera77]

Honesty, I'd try to find an 86/87 harness, or even a 88/89 harness. The 90/91 is a lot different.

[mobydick]

Chiltons books usually have all the wiring diagrams in them.

[gadget73]

it can be done, just have to ID the wiring. Helps a million if you have the proper EVTM tho.

If it helps any, the wire colors that are related to cruise control are dark green/white,white/pink, gray/black, orange/yellow, light blue/yellow, light blue/black and light green according to the 91 Mark VII book. The gray/black, white/pink, and orange/yellow probably go to a connector that looks just like the one plugged into the cruise servo now. The light blue/black, light blue/yellow are the inputs from the steering wheel buttons. Not sure where they may be found, but I'll guess its in a connector that has other wires that you do need to make it go. Dark green/white is from the VSS and is somewhere in the trans harness. You do need that one. Light green is for the brake switch. Don't need that one, but it will give you a dummy code for not pressing the brake pedal during the self test, even if you do hit the pedal. No real effect otherwise. If someone has the 1991 Vic book, they should be able to tell you which connector those wires are in.

[zx4133]

Thanks to everyone for the help and advice. I really appreciate it. The weather (and my crazy work schedule) has prevented me from working on the wiring the last few days but I'll be back at it soon. I'm going to take some pictures as well so you guys can see exactly what I'm dealing with. The first step that I'm working on right now is identifying what each connector goes to on both the 91 harness and what I have left of the 86 harness. When I got the 86, the engine, transmission, and computer were already removed. The main engine harness was also removed. From what I can tell, the engine harness connects to the vehicle at 2 points, one being where it plugs into the computer, the other is a wiring harness that goes through the firewall to the dash. The engine connector was simply unplugged, but the other harness was cut about 4 inches outside of the firewall.

The next step I have planned after identifying each connector on the 91 is simply to find the corresponding connector/wires on the 86 and splice them together. I know I'll have extras wires here and there and not everything will plug in all nice and pretty. But I plan to solder connections and use heat shrink tubing and do everything the right way. The biggest holdup right now is the wiring diagrams. Gonna try to get my hands on some EVTM's.

[85crownHPP]

but the other harness was cut about 4 inches outside of the firewall.

Ick.

If they hadn't cut it there, you would see a big connector on the drivers fender well where the ECM harness is supposed to join the body wiring.
Bad news is, other things could have gotten cut. I'm wondering what's left of your alternator wiring... And do you still have the big harness on the drivers fender for your forward lighting?

[gadget73]

the best thing to do here might be to junkyard hunt for an 86. that would get you exactly what is missing and provide a reference for how yours ought to be.

[zx4133]

86's are kinda hard to find here in Orlando, but I'll go that route if I have to. The original 86 cruise control wiring, forward lighting wiring, and most of the A/C wiring appears to all be there and be intact. It's basically just the engine and ECM harness that are missing. As far as the alternator wiring, I have all of that intact from the 91 harness. Is it not useable on the 86? Is that why you asked about it 85crownHPP? Cuz that might be an additional headache if it's not compatible.

PS. I ordered factory EVTMs for both the 86 and the 91 so that should help. Should have them in a few days.

[85crownHPP]

Nah, it wont be hard to wire the alternator in. I think the green wire (for the battery light) and maybe the yellow wire join into that harness that was cut, so its just 2 more wires to dig out of the stump that's left.
If you have all the alt. wiring for the 91 that's good. I wouldn't want to try to splice back together the charge wires, but it sounds like you've got that in tact.
If you can put up pics of what you've got it will definitely help, and I will get you those pics of my 91 EVTM this weekend, promise!

[zx4133]

If you can put up pics of what you've got it will definitely help, and I will get you those pics of my 91 EVTM this weekend, promise!

Thanks a lot man - that would be a huge help!

And I'll take some pics of everything as soon as this damn rain clears.