If it won't crank when you short the two STARTER SOLENOID terminals AT THE starter (please be SPECIFIC) then you have got the trouble down to just a very few things
1....Forementioned cables and connections. You can NOT test these "not under load" with a voltmeter
2...Bad starter
You did not mention doing what I asked
TURN ON THE HEADLIGHTS.
Then jumper the solenoid. What happens?
There is a VERY GOOD REASON for being SPECIFIC
When you turn on the headlights, this LOADS the circuit, but only some amount. The headlights should light nice and bright. This at least shows that you have some continuity in the electrical system/ cables/ connections, and that the battery is able to provide SOME current
NEXT jumper the solenoid
Does the starter crank the engine? No? Do the headlights dim WAY down? Not at all? go clear out?
If the lights dim not at all, you probably have a bad starter, BUT CONFIRM
If they go clear out, you most likely still have cable/ connection problems, or a defective battery. YOU CAN NOT TEST a battery NOT UNDER LOAD with a voltmeter