Biohazard

Got a little excited and thought I'd stick the key in and see if she would turn over. Answer is - no. I get the audible click, sounds like the starter solenoid is being energized, but not even an attempt to spin the rotating mass.

This led to me pulling out the starter and testing it on the floor of the garage.

With 12 volts from the car's battery via heavy duty jumper cables, the starter engages and spins like a champ. (while I was there, I went ahead and tested the other one I bought and it, too, works fine...smoother, actually, than the one in the car).

So I'm thinking - maybe I need better ground cables? The positive lead to the starter and its solenoid are new. The battery is healthy - no concerns there. The negative cable from the battery to the left cylinder head, however, is old and shitty looking and I do not yet have a ground strap bridging the right cylinder head to the firewall. You guys think I just need to get my grounding situation in proper order?