Electrical Too Many 90 V8 Harnesses Convert to 89???


New Member
Jan 5, 2024
Concord, CA
I've read up and down forums, and everyone is curious if it works... But seems no one ever commits. I have an 89 and a 90 car, so I can verify my finding, also have (3)90 V8 harnesses along with two harvested 87 harnesses.

I'm not desperate for one for myself, I just don't see how the air bag plugs keeps from working in 87-89 cars. Both have MAF, both have (2)dash connectors, all identical connecter elsewhere. Also consider the plug and play harnesses and how all computer nearly swap between CA88-93 cars(little alterations depending on Manual computer)

I know this wouldn't work with 91+ as easy bc the one connector dash harness and then later FP relay on P/S fender.

I am posting this for two reasons, hear anyone's findings and report mine if I have to go about it myself. 90 harnesses seem to be easiest found, and they are much harder to flip.
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Well, what I figured, but I've never heard one person say that a 90 would swap in a pre-90. I can just leave, cut, or rip out the airbag connections completely and call it an 89 wiring harness??? Anyone know the contrary?
Goes without saying but the easiest way to figure this out would be to have the wiring diagrams for an 89 car and a 90 car. My guess is the dash wiring pin out may be different but it may only require the connector to be repinned to match.

As stated the center crash and passenger side front crash sensor wiring just passed through the 90 harness so it could be removed, taped back, or just left.
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So, likely only the dash connector needs to be repinned at worse. I saw someone mentioning they had a wiring diagram for an 89 in a very old post, but I'd like to figure this out. I can't believe no one has navigated this territory, some reason there seems to be more 90 V8 mustang then all I have ever ran into. I probably count 4 90s I have ever owned, 87, 89, 91, 93.
There are subtle changes to the harnesses over the years. May only be 1-4 wires or so, but they are worth noting.

There’s an 87-early 88 harness. A late ‘88 speed density harness, an 88 mass air harness, and the ‘89 harness. That’s for engine harnesses. The plugs are all the same but there may be an extra wire or two or one missing.

1990 was a major change with plug connectors changing as well as colors. While it’s not impossible to convert it, it will certainly require some commitment to studying the wiring diagrams and ringing the wires out with a meter to confirm what they do and checking the pinouts of all the plugs to make sure you move the wire to the correct spot. The latter is the biggest challenge because the EVTMs do not show the color/pin arrangement of the intraharness connections.

When time = money, you can come out ahead by selling off the harnesses you don’t need and buying the one you do. Problem is nobody ever identifies the engine harnesses properly. I often see “87-93 harness” and if lucky I see it broken up into 87-89 and 90-93 harnesses. Nobody ever lists it by the specific year and configuration.