

Is the starter getting juice
Tighten the battery terminals, they shouldn’t slip off at all.
Your wires could be rusted enough to cause problems. You should have a ground wire that goes from the engine block to the negative on the battery, sometimes using the body/frame to complete the circuit. If that’s rusted or is loose then you’ll have something’s working but the starter won’t.
Some custom designed stuff I ordered just landed today. I’m about to pay an extra $300 because of that fool.