not getting full voltage to starter
 

The truck starts great until two days ago. Now it get 12 volts going to the ignition switch but 3 or 4 volts to the purple starter wire. I suspect the problem is the ignition switch but if anyone has some advice before i change the switch out.
truck is 1968 c10 that i did an LS swap on.

Re: not getting full voltage to starter
 

Were those voltage measurements taken at the ignition switch connector? If so, it sounds like you are on the right track suspecting the ignition switch. About the only other thing to check would be the terminals in the ignition switch connector ... check to make sure the terminals aren't tarnished/corroded and that they're fitting snugly onto the blades of the switch.

Re: not getting full voltage to starter
 

Always measure voltage to ground. I'd measure at the input and output at the ignition switch, and the NSS. The purple wire controls the solenoid, which controls the starter. 12V is no bueno. See the link.
Make sure the engine is grounded (not the alternator bracket, or whatever) with the big - cable.

https://www.google.com/search?q=batt...utf-8&oe=utf-8

Re: not getting full voltage to starter
 

I always like to jump the starter solenoid when I troubleshoot the start circuit. If the engine turns over good it eliminates the starter, the solenoid, and the battery cables and points to the control circuit--Key switch, NSS, and the wiring.

Pull the coil or distributor wire to avoid engine start by accident.

If the engine turns over fine then jump from the red wire on the horn relay(this wire comes directly from the battery alternator junction and is full 12 volts) to the NSS terminal wires and see if the engine turns. You can also check the NSS this way with the gear selector in park both purple wires should turn the engine and when put in gear only one of the purple wires will turn the engine. Remember PULL the coil wire

If these checks work then the problem is in the key switch or the harness plug like Ray said.

Re: not getting full voltage to starter
 

So I checked the wire going to the starter and found it was grounding out. That explains the dead short. I move the wire and it started right up. It had started twice for me while I was trying to figure it out then wouldn’t start again so I was confident the starter was good. Thankfully I will rerun the wire and make sure it doesn’t rub. Thanks for you your advice.

Patrick