Project car: assuming bad starter relay. Confirm?
HOW to do this
1. Jumper (using screwdriver, etc) between the two large posts. That is, the big stud and the big square solenoid terminal..... The starter should operate so be careful you have it in park/ neutral. This proves the starter, the battery cables, and the big wire down to the solenoid are all OK
2...Remove the push on flag terminal (wire). Jumper from the big stud to that flag terminal. The relay should operate the starter
3...If not, maybe the relay is NOT GROUNDING. Loosen the mounting bolt and retighten. Then clip a jumper to a good ground on the engine, and jumper into that solder spot on the top of the relay that jumpers over to the case. Now, use a screwdriver or jumper to again jump from the big stud to the flag terminal. If it does not crank, replace the relay If it does crank, either the solder jumper to the case is broken, or the case is still not grounding to the body
I tend to get "too deep" quickly. I wast no time grapping some "alligator clip" jumper leads, my meter (Fluke) and a test lamp I highly recommend good used Fluke meters over much of the HF freight stuff you see. Seen too many of them fail and become grossly inaccurate. I've bought used Flukes for as low as 25 bucks up to about 50, a bit more for a "juicy" one.