I just got a 87 Dakota with the 3.9 in it and it won't crank at all. Put a battery in from one of my other cars, tested the headlights before trying to start it, and they worked fine. As soon as I tried to start it did nothing, and no more headlights. Put a multimeter onthe battery and its still reading 12.4 volts. What's going on?

 

I can't see your truck from here. I'd guess you have a short somewhere in the starter circuit and took out a fusible link and/or the fuse for the starter in the relay box, found up front, driver side, in the engine compartment. Also, see the FAQ for pertinent info on "the splice".

 

Turned out to be the positive water going to the terminal was breaking, so I put on a new terminal and now it cranks! Now it needs a fuel pump relay