Everything starts with the ignition key. Then it should go to the starter solenoid. Obviously the engine can get current, so go back to square one and that is the ignition key. Follow the current path until it breaks. I am curious. When you jump the starter solenoid, is the ignition key in the "run" position or "off position"?
Solenoid is good, and the wire is good because I'm jumping the solenoid by just connecting the two posts on the solenoid. Just to make sure I wasn't crazy, I even sent 12v to the solenoid pins (the ones that connect to the key switch) as well and it starts right up as well.
There is your break I mentioned. The solenoid is not getting current from the starter switch. With your multimeter on the starter switch, does it send current to the solenoid? Does it send current to the ignition? Probably easiest to just replace the starter switch.
Dave