Yup starter stuck engaged.

You really shouldn't have a negative wire going to the alternator unless it's a smallesh one for the regulator...

Your vehicle needs a serious ground wire!

This ground wire has to carry ALL the starter current, which if this is a V8 would be on the order of 500Amps!! You should have a wire going from your battery(-) to a stout bolt on your engine block.

It should be about the diameter of your little finger.

From your battery there should also be a relatively large wire going from the battery (-) to your car's body. This wire can be about 1/3 the diameter of the other wire.

What happens is your starter is not getting enough current. So when you go to start the engine, the starter gear gets shot into the ring gear on the way to the starter gear turning, so your ring gear turns, so your engine turns.

Well the starter solenoid flings the starter gear into the flywheel... then when the starter goes to turn the engine BIG TIME CURRENT is demanded. But because of your crummy ground cable it just starts to turn and jams up. This keeps the starter motor turned on requesting that 500 Amps but because it can't get that it just sits there stuck often not allowing the starter gear to retact and turn off the starter.