Keep in mind the ACC fuse in a new harness with prewired fuse box has nothing to do with the old ACC terminal on a 55-59 solenoid ignition switch or a new ignition switch ACC terminal.
Did your harness have instructions for an exciter wire? If so, where did they have it wired?
"It is a custom harness and the exciter wire is connected to the ACC side of the fuse panel so it is separate from the ignition hot side"
There is no "ACC side" on the fuse panel. There is an ACC fuse, not normally used. There are fuses that are "always hot" and there are fuses that are switched to be hot by the ignition switch. The ACC is one of the fuses that is switched. It is no different than the other switched fuses. It's just an extra fuse for choke or some odd ball thing. I am going by the assumption that a run-on is a miswire. Due to misunderstanding of the ignition and such. A starter with no "R" terminal or something like that. Folks trying to make old ignition parts work in a 12V conversion with a new 3 wire alternator and new harness. It can be confusing. I do want to say that if a bulb or a diode or a resistor fixes it, do that.
That's why it is hard to figure out why some no bulb folks have run on and some don't. That's all I'm trying to figure out. You can be the answer. You are so close. If you could transfer that "ACC" wire to IGN ON, with blade in the socket, you could prove something. Then if it runs-on you could put bulb in and try that. All you need is an alligator clip on an existing wire to the coil positive or ballast resistor, so as to stop motor in case.
OR...........one of these days I will find someone with a 3 wire 10si, no bulb, with run-on who is willing to try a few things. Now that I'm obsessed.
