My '74 in progress has an intermitent problem with the AC/blower and the "GEN" idiot lite. Sometimes the blower works as it should and the idiot lite goes out when the engine is running. Most of the time, the blower will not run and the idiot lite stays on. The alt. is charging correctly, I just had it rebuilt, and this happened before and after the rebuild. I can connect 12v from the ACC terminal of the fuse block to the large Brown wire under the dash just to the right of the gas pedal cable and make these things work. The brown wire is paired with a pink wire at a connector and the other side of the connector is 2 yellow wires that go to the heater blower resistors and the other goes to a sender on the right side on the back of the block. I have downloaded the wiring diagrams but they are slightly different from my vehicle.
Any ideas appreciated.

It sounds like a loose connection. Have you checked all the wire ends?

Bad ground from the gauges to BODY may be the cause. The GEN light and the left signal indicator light stayed on any time the ignition was on in my old '69. I made a 16 gauge ground wire from the car body to the back of the gauge panel and there was happiness in my village again. Just a thought.