In stock configuration:
The truck is mostly 12v. There is a 24v starter, and 24v is fed to the GP resistor (back of the engine bay, but yours is missing), and there is 24v going to the starter relay under the dash, a 24v feed to the Gen2 idiot light and the voltmeter, and one to the fuse block.
Everything else is 12v.
Thank you. Do you think I can get back to 24v with my configuration?
In your case, you have such a hacked mess that it's really going to be hard help you figure it out.
But we'll try!
Thank you
That wiring harness is almost certainly 12v, BTW. One of those GP controller cards was designed and manufactured by one of our members here. CUCV Electric was his company name, but now he sells them through Hillbilly Wizard. Unless it's been fried by your P.O. doing stupid things, it's gold.
The PO said it wasn’t installed. This is probably dumb, but where does it go?
Let's start there. Trace the wires from your glow plugs and see where they go. Post pics. You are trying to find out how the P.O. has got them hacked up.