My oil pressure light will come on only when the ignition is off. It will go on sometimes hours after I have used the vehicle. Not sure where to start.

Also the car has begun to run rough like crazy for the first couple miles. Never stalls, but misfires until she is warm. I get some hesitation at high speeds. Could there be something wrong at the cold start injector?

Thanks.

That was what I was afraid of. I don't know how much $$$ I can keep pouring into her. She owes me nothing really. I will see if I can do thick simple fix, rather than the whole harness. I know a new harness will require someone more mechanicla than I ... a mechanic.

Just do it one wire at a time. You don't need to buy a whole harness. Just check each one in turn for continuity, overheating, fraying, etc, and then solder in a new section back from somewhere sound.

Last week I re-wired the oil pressure circuit on my 85 245. It was a problem caused by the rotting engine harness. The wire that runs to the oil sender comes out through the firewall and is one of the wires (black) that is included in the big connector at the center of the engine on the firewall. It goes directly from there to the oil sender. I simply cut the wire and soldered a new wire on. From this point I routed the new wire around the engine, over the right side strut tower and down alongside the ignition module and zip tied it to the existing wiring. I cut the old wire loose from the connector for the sender switch and soldered the new wire on. I covered all of my splices with shrink tubing, and my problem was solved. Don't try to pull the old wire out because you may damage the old insulation on the remaining wires in the bundle. I also did the same thing to the (small red) alternator wire coming from the dash and paralled it with my new oil sender wire. It's also located at the big connector and goes straight to the alternator.
Hope this helps
steve

Check the under-the-engine-front harness for damage to it and to the wires within. Disconnect the negative battery cable before messing with that harness.

Good Luck,

Bob

:>)

Underneath the alternator is a favourite spot for corroding wires. The wire from the pressure gauge sender is taped up with the thick red (always live) cable to the alternator, and jammed behind the alternator bracket. If the alternator wire corrodes and gets hot it melts through to the sender wire, and shorts, hence the false light signal.
But I believe in the US you have problems with the whole harness degrading, which might explain your other symptoms.

Harness degradation time...