Hi,
I've got a 78 f150 I've replaced the starter in it 3x in 2 months. Well this last time before replacing it I was bypassing the ignition by jumping it through solinode, well I noticed the wiring got really hot. So I replaced the starter and now when I turn key to accs it imidentaly starts trying to fire up until I turn key off but never does fire up all the way? Now the wire that connects the solinode to I believe the alternator "fusable link" got really hot and melted around the connector could this be the problem?

 

A '78 doesn't have a starter solenoid; only a starter relay. Click these & read their captions:

. . .

This shows how to put a solenoid starter (PMGR) into an older truck, but doing that WON'T fix your problems.

 

check the grounds and if you have acces to an ampere meter measure the amps.
also check your ignition (and the wire getting 12V to the coil instead of the 8v when it's already running)