I have a 1988 ranger STX 2.9l and I tryed to start it a few time bc I replaced the ICM and wanted to see if she’d start. When I did my final crank before I’d have to get ready for work all of a sudden it’s wouldn’t shut off with key off so I ran to the battery disconnected it. I sat and waited for a few seconds before reconnecting it and when I did it started to melt the negative terminal on the battery as if it got so hot to melt it. I have no idea what’s going on or we’re to start looking for problems. Please help

 

Welcome to the forum

So ignition key didn't shut off the power to the system, I would start there, ignition switch is under the steering column above brake pedal area, these older switch would split at the seems but could be held together by zipties
Hard to find replacements
The key itself just turns a gear that causes the actuator rod inside the steering column to slide the ignition switch into its 4 positions, ACC, OFF, RUN, START

Disconnecting a battery cable shouldn't have shut off the engine
Once an engine is running the Alternator is supplying ALL the voltage, battery is being charged by alternator so is "off-line"
So if disconnecting battery worked it means alternator was either shut off by the key or wasn't working

Heated up battery cable, either one, means there is a short between the two terminals of the battery, could be ignition switch
But pretty much all electrical systems in a vehicle have fuses or fusible links that should "melt" when there is a short, if they don't then the WIRES MELT, get super HOT
Nothing jumps out on description that would narrow down where a short might be

Make sure no one has replaced any fuses with pennies or nickles, lol, or in the good ol' days, 22 cartridges