In my 1988 F150 I was having a problem with the engine turning over. Sometimes it wouldn't quite crank or would barley crank. Replaced the battery this week and still had the problem. Replaced the pos. lead and the starter soloniod and it started great. Turned it off and then started it again. Did this a few times. Never had a problem. Went to run an errand a few hours later and the starter wouldn't disengage and the pos. lead from the battery melted through the plastic before I could disconnect the battery.
Assumed it was because the soloniod I used had been in my truck for a few months did the same swap (Sol. and (+) lead). Started great a few times, then when I went to start hours later, it the same meltdown happened.
I've checked the wiring diagram in my Chiltons and I think I'm right. Leads to the altenator and the wiring harnesss off the front terminal with the (+) lead and only the starter hooked up off the rear terminal.
Hooked it up after work and it started great. No issues, but I didn't change anything. I'll start it again tonight after a few hours and see if it melts the (+) lead again.

 

The cheap *** solenoid is fusing together.

 

Change your positive cable to something a few gauges larger as well as the cable from the solenoid to the starter..Make sure the grounds are nice and clean. I run 1 from the battery right to the alternator. Less resistance makes everything last longer in the starting/charging circuit. I used 5/8" copper on mine and I'm running a battery 2 years past it's normal 2 year lifespan. I can leave my headlights on for 2 hours and still fire her up with no problem My solenoid never gets hot and I still have the same starter that came with the truck off the assembly line. (24 yrs old! lol)

DEFINITELY buy a quality solenoid.,..

 

I've got the midgrade solenoid with life time warranty from O'reilys and 4 gauge copper running to it. I'll run though it tonight. Thanks