01 dodge 2500 Cummins diesel. Started off it turned over fast but wouldn't start. I changed a VERY CORRODED terminal end and it started. I drove it across town and shut it off then it went back to the same thing, turned over but wouldn't start again. Visually inspected cables and changed all the terminal ends but it didn't help. Now it won't even turn over. No click or anything when I turn the key. Hooked a wire to both posts of the starter it only sparked a little no click or spin. Took both batteries and the starter in for testing but they all tested good. When I put the starter back in it did turn over once slow then nothing.

sounds like either the Solenoid trigger wire is having issues, or a possible voltage drop on the battery cable to starter. Could also be a grounding issue.

A quick test I've done in the past is by using a set of jumper cables.

Connect one end of it to ground and positive of the battery.

On the other end, leave the ground side disconnected, and connect the positive end to the terminal on the starter where the positive battery cable connects (the big lug). Try to start it. If no change, disconnect the cable from the lug, and connect the ground end to the starter housing or block. Try to start it again. If no change, connect both to the starter (positive to battery cable lug on starter, ground to starter chassis or block) and try to start again.

If no change, leave them connected, and use a jumper wire from the positive terminal lug (where the jumper cable is connected) to the small post for the starter solenoid. Touching this connection should result in either the truck turning over. If it does, then start backtracking the starter solenoid trigger circuit.

DANGER!

**WARNING** EXERCISE CAUTION: YOU ARE RESPONSIBLE FOR YOUR OWN HEALTH AND SAFETY! ENSURE TRUCK IS IN PARK (auto) OR NEUTRAL (manual), PARKING BRAKE IS SET, AND WHEELS ARE CHOCKED PRIOR TO TESTING. THIS TESTING CAN BE DANGEROUS SHOULD THE VEHICLE TRY TO MOVE DURING THE TESTS.