The blue wire should be sender to gauge, no clue (unless) why it would go to starter.
The black wire has been added(?). Check for voltage on the black wire with ignition on/off. The shop manual shows a W/O purple wire to the same side of the starter solenoid as the yellow wire. I believe the W/O ppl wire is a resistance wire to drop the voltage to the coil when running to 9v. IIRC I've also seen the the resistance wire spliced into the yellow wire in the harness. Hope that helps.
Larry
The photo may not be clear, but I assure you that the blue wire does NOT go to the starter. It goes from the oil pressure switch to the dash gauges (somehow).
Also, I cannot find a ballast resistor anywhere. My FSM doesn't show a ballast resistor in the wiring diagram for the C10 trucks.
I will pull the wire harness and carefully inspect the wires for a splice. I am unsure if this engine harness came with the 250ci from the donor '71 truck OR if it is the original harness from the '66 truck (which had a factory 250ci).
I did check the coil with the starter cranking and got better than 10,000 volts at the coil's negative post connected to ground.
I get 12.74V at the coil's negative post with the key turned to IGN but not cranking.
I'm thinking maybe the coil isn't bad after all.
