Does the starter work when you jump the two heavy solenoid terminals?
Could be a bad starter, drawing too much current.
Could be a poor ground. Unplug both small terminals. Ground one, then jump the other to the bat + or the heavy bat. terminal. The solenoid should work.
Did you check all the battery cable connections?
It ain't rocket science!
'Course if yer house has more wheels than yer truck...
" Old age ain't for sissies "