Start troubleshooting from the starter.
- Make sure you have the large battery cable tight on the starter lug.
- (then make sure its in neutral) Use a small jumper wire from the large lug over to the small S terminal on the starter. Just hold the wire and touch it between the two points, which will apply 12 volts to the solenoid. If it turns the engine over, the starter is working.
- Now take the wire off the S terminal and put a voltmeter or test light on it. If you don't get 12 volts when you turn the key to start, you have a break somewhere. Look for breaks in the wire where it runs through a metal tube up behind the exhaust manifold and to a point behind the valve cover.
- If no breaks are obvious, then go to the neutral safety switch and pull off the plug. Use spade connectors on both ends of a jumper wire. First plug it into the ignition switch side of the plug and use a test light to make sure that you get 12 volts in start.
- If you do get 12 volts, use the jumper to bypass the neutral safety switch. If that works to turn over the starter, you just need to make some adjustments in the switch. If that does not work, you have a wire break between the neutral safety output wire and the starter solenoid. You can trace and find the break, or just run a new wire.
- If you don't get 12 volts in start at the neutral safety input, you have a bad ignition switch or a wire break between the switch and the neutral safety.
You could also reverse the process and start troubleshooting from the neutral safety switch. However, on a manual trans its probably under the the truck and not much easier to reach than the starter.