Squaty,
Your blower motor is held in place by about 6 screws and one of those screws has a terminal under it for the ground wire. Could this plug be for that ground terminal?
And you say all the TCS wires are are accounted for, but how about the one that goes down to the tranny?
The 3 wires (blower, blower ground and TCS to tranny) are all I know of with single plugs on the starter side such as you mention.
Surely it's not the wire with a single plug going to the CI hood, is it?
Just to touch on the orange wire. When I re-taped the wiring harness on my son's 71, I discovered an orange wire, that had been cut off, in the harness that had been covered up by the factory tape. This would have been the blower motor wire for a non-ac car. A factory ac car has a seperate wiring harness for ac which includes a wire for the blower. With the aide of a wiring schematic, it took me a while to figure this out. Anyone else come to this conclusion?
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