[WorkinLonghorn]

If you have electronic ignition (HEI or similar) you need to have 12 volts to the distributor. Coming out of a stock ignition switch I believe there are 2 different wires to the solenoid a purple resistance wire that reduces the voltage for a POINTS TYPE distributor and another one (orange and purple?) that supplies 12 volts during starting only. IF YOU HAVE HEI you NEED 12 volts constantly to run at all so you need to replace the purple wire (or whatever color the resistance wire is- look at the solenoid) with a regular wire that is not resistance wire . Very simple procedure. Check with a volt meter if you want to see what the voltage is to the distributor with the switch in the "run" position. Should be close to 12v not 9v.
I'm no mad genius with this electrical stuff but I think I have this right. It's what I have read and it worked on my truck. If you are getting 12v then you need a new switch. You won't see a problem from the outside. The contacts internally could be oxidized or burnt. -BA