79 Bronco wont start?

i have a 79 bronco with a 400m and c6 trans. it started fine 2 days ago but it needed a new alternator. so i hooked it up to the charger after i installed my new alternator. and it woulnt start. i have been asking on a few other sites and they all said check the solenoid, power and ground wires, and starter. so i put a new solenoid on it, and still nothing, i replace the power wire to the starter yet again nothing.. then i pulled the starter and hooked a power and a ground up to it turned the key and it worked fine. so i put it back on and ran a ground to it i am 99% sure everything is hooked up right. and the battery is a fairly new optima that i just pulled out of my other truck so it is for sure a good battery.. but it wont do anything when the starter is bolted in... does anybody have any possible idea what could be wrong with it? i have tried just about everything.