When the key is in "acc" or "on", everything is fine. When I turn it to "start", it's not so good. Sometimes it starts just fine. Sometimes, I get a repeated clicking like a starter solenoid, sometimes everything electrical dies - radio turns off, lights go out, horn doesn't work. I don't understand this, since the horn should always be hot.

 

Let it sit for a few minutes, or unhook the battery cable for a split second, and you hear a click, followed by the electrics coming back to life. Is there some sort of circuit breaker responsible for this, and what could be offending it?

 

I threw a new, used ignition switch at it, but that didn't change anything. Battery tests nice and strong, I don't see much corrosion anywhere. I'd really appreciate any insight you could offer.

Check all connections at battery, alternator, and starter. I'm betting there is a bad connection, dirty connection, or crimped wire somewhere.

 

The starter could also be going bad.

 

Next time it does it, have a hammer and screw driver (or other long object) handy and smack the starter/solenoid. If it starts after that, then the starter is going out.

 

A bad starter/solenoid or connection there is my guess.

Sounds like a bad ground cable.

The starter solenoid clicks when it doesn't get enough juice. You need amperage and voltage to make the starter motor turn. So even if you get 12V at the solenoid you aren't getting the amperage needed to power it.

Check all the connections. Make sure the engine to frame cable ground is tight and not broken. Make sure the frame to battery ground cable is tight and clean. And make sure the battery positive on the starter is tight.