Hi will a an early harness for the starter/coil/oil pressure switch work in a 75' unmodified?

The early harness has two extra wires that appear to be for an aux. fan.

Thanks,
Dan

Yes, it should. The 70-71 fan wires were in the engine harness that were moved to the main harness in later cars. Maybe Jeff B will chime in here on this.

Thanks Mark, I may decide to add another blower in the near future.

It will work but there are a couple differences. The heater fan connection is different than the later cars, but I think it will work, there is another ground wire to deal with. The starter wire gauge is smaller, it was enlarged in the 1973 and later harnesses (all wires in my new harnesses are even larger). And the oil temp connection is on this harness..I suppose you could just ignore that wire...tape it onto the harness.

It will work but there are a couple differences. The heater fan connection is different than the later cars, but I think it will work, there is another ground wire to deal with. The starter wire gauge is smaller, it was enlarged in the 1973 and later harnesses (all wires in my new harnesses are even larger). And the oil temp connection is on this harness..I suppose you could just ignore that wire...tape it onto the harness.

You can compare the two schematics on my wiring harness website.