she had been having trouble starting with a hot engine, but would always start fine when cold. So today I went to give it a cold start, and nothing! the horn wouldn't even blow. so I checked across the battery with a meter - still nothing. I opened the caps to check the water and it was boiling and bubbling in the battery. less than a minute later the battery was disconnected. It was hot as hell and I didn't want that blowing up in my face. I found strong continuity between the battery cables, that can't possibly be good. I took the starter cable off at the relay, and I'm still getting continuity between any cable, to any other cable in any configuration. but for some odd reason, the battery which is now connected to nothing is making 12 1/2 volts. Which combo of contacts should have continuity, and which ones should be open ?

 

Well, at least it didn't boil the electrolyte completely out of the battery.

No continuity across any positive/negative combination is good UNLESS there is a device with a coil still connected to them. For example: you should never get continuity between the negative and positive sides of a lighting circuit IF the bulb is in the socket and not burned out. Take the good bulb out and there should be no continuity. The same is true for any electrical device containing a coil. So, motors, solenoids, relays, lamps, basically anything in the truck.

With the battery disconnected you should be able to read continuity on the positive cable from the battery terminal to the relay on the inner fender that holds the other end of that cable. There should be NO continuity beyond the terminal on the relay that holds the other end of the battery cable. The second large terminal should only have continuity from the relay down to the starter. The negative battery cable should have continuity from the battery terminal to any bare metal surface on the truck with a few minor exceptions. Any continuity across positive and negative battery cables is indicative of a major short circuit. A fried starter motor could potentially do this. The windings are big enough and strong enough to maintain a connection even with 600 amps @ 12VDC (typical battery amperage and voltage) running through them. The question would be what CAUSED such an event unless the starter motor had a winding break and short against the body of the motor. However, the fact that this boiled the electrolyte in the battery indicates that the relay on the fender was not fully disengaging either. Either way, finding that condition when you did was fortuitous because left unchecked the explosion or caustic meltdown from a car battery is dangerous to say the least.

With the fact that you were having trouble with hot restarts you could have had a starter suffer a thermal breakdown.