Starting problem......sometimes dead!

[72lb4x4]

Start with cheap and easy... Things may look good, but...

Charge the battery with a 2A for 12-24 hours
Fix the grounds
Fix the + connections
Get a DVM (digital volt meter) with of course the other basics and and figure out what it means and how to use it.
Don't spend any money buying ignition switches before the above.

The longest answer above is the toughest and what will lead to the actual problem.

Magic bullets (randomly replacing parts or shotgunning) will usually lose money or win the lottery (got lucky).

Get a meter, research (autozone.com for example), a wiring diagram. think, listen/read, but don't believe.

All that said, I'll offer a guess...

If the problem is intermittent without a difference in heat, suspect a loose connection. A wiggly connection can stop (the truck,or) whenever whenever it feels like it.

Without a voltmeter, and an understanding, you can only replace parts. Get those 2 things and understand, and, well then the real frustration begins...

Electrical problems are maddening, but you can spend money, or time, or both fixing them. At home, only money and time actually solve the problem. They will drive you mad.