I'm trying to resurrect a Case 580C which hasn't run in a long time. Got it running, but now starter switch doesn't make starter turn over. It doesn't try to engage the starter solenoid, it's like there's something that's not letting it get the signal to the starter. I pulled off the shuttle fwd/reverse wire plug and tried to jumper across it and remove the jumper, but neither make a difference. I've cleaned both ends of the positive and negative wires coming off the battery and made sure the battery's good. There's almost no voltage drop when you push the starter button. If I jump across the terminals on the starter the engine cranks fine. Should I look at the starter switch itself or something else next?
Electricity is invisible, so you need some sort of tester. A simple testlight from Harbor Freight or the parts store will work for you. Then you can clip the wire of the testlight on a good metal ground, and then probe the switch to see if it has power. You can also probe the forward/reverse plug, and press the start switch and see if you have power going to the switch plug. Here's what the tester looks like.
Remove the ignition switch. Then check for 12 volts on the stater terminal with the key turned to the start position. If there is 12 volts available there, there is a problem with the wire that goes from there to the solenoid terminal.
I pulled the starter button harness. With the key turned on one leg has 12vdc. I jumpered across to the other leg and the starter still didn't engage. My circuit tester said there was around 12.6VDC where I measured. But I still had the shuttle switch unplugged. Does the shuttle switch to be closed to enable starting or open? I suspect closed, so I can try to jumper across it to test?
All machines have neutral start switches or lock of some sort, that prevent them from being started in gear. Yes, closed. Open switches do not pass current. I would use an ohm meter to check it. If you don't have one, a tester like Franklin posted will work quite well. The circuit has to be energized for that tester to function.
Ok, it works now, here's what I did. I put the jumper back in on the shuttle neutral harness to guarantee it is closed and therefore passes current. Then I took the starter button out of the dash. Special place in a fiery lake to the idiot engineer who didn't put a captive nut on the back side of the dash screws so you need a 15" extension and 5 guesses what the nut size might be. After the shuttle harness was jumpered, I jumpered the two wires on the starter button and the starter began working! Then I plugged the shuttle neutral switch back in and it still worked. I cleaned the terminals on the starter switch and plugged it back in the harness and now the starter engages consistently. I also put a tiny bit of grease and WD-40 on them. Thanks all for the help!