Got a list of things I need help with.

[DrHax]

Would a way to test if the solenoid is dropping voltage be to run a screwdriver against the terminals ghetto style to bypass the solenoid all together?

[DerekTheGreat]

No, like gadget said those relays tend to work or not work at all. They can fail in the "permanently working" mode which kinda solders the two posts together and the magnet/spring thingy inside can't break the connection so the starter ends up getting juice even when you don't want it to. Anyway, If you don't want to do a voltage drop test, just replace the battery cables from the battery to the starter solenoid and then from the solenoid to the starter itself and then the ground from the engine to the battery & see what that does. With GM, batter cable corrosion is a big deal, at least with their trucks. I can see the end of my positive battery cable terminal swelling from corrosion. Lazy me will try to put off replacing it in the spring but wouldn't be surprised if it can't supply enough pixies on the 1 or 3 random days when it's -2F outside.

EDIT: Also, if you have those ultra shitty $2 battery post things from Autozone that clamp down on the battery cable, make them fuck off. Those are absolute garbage and any car we acquire that has them, that's the first repair we make. Ends should be soldered on like the factory units were, helps stave off corrosion & ensures better flow of the pixies.

[DrHax]

What’s the length of the switch to starter cable I should be looking for?

[sxcpotatoes]

Looks like it's STANDARD MOTOR PRODUCTS A514L (I also see it listed elsewhere as A51-4L), I don't know the length.