I have 1960 Chevy Stepside that I just rewired from front to back with original style wiring harnesses from Classic Parts. When I turn the key (to the first position) the starter kicks in, although nothing should happen until the second position (i.e, hold until start). I'm confident everything under the hood is wired correctly. I have a wiring diagram and have double and triple checked everything, so I have to believe it is a problem under the dash.
Interestingly enough, the new underdash wiring harness has a purple wire that runs to the starter (from the switch) but also has a "loop" in it (with a jumper), which I assume was an option for a neutral safety switch. In any case if I pull the jumper from the loop the engine doesn't turn over. I'm not sure this is relevant but at least I know it is the starter wire.
Any help would be greatly appreciated. I'm dead in the water at the moment... Thanks.