Interesting, the last owner I saw moved the starter relay up to the firewall and used some generic relay.
You are correct. Per some of your photos in
this thread, your original starter relay has (more or less) been bypassed.
The solid (no stripe) purple wire you see coming out of your original starter relay is the one that we noticed is cut on the engine side of the firewall, shown below... If you wanted to remove the previous owner's generic relay and return the truck's wiring to the stock starter relay configuration, it wouldn't take too much repair work.
And my voltmeter doesn't work.
You'll need to verify that the orange wire connecting the 24v voltmeter to the fuse block is intact from end to end, and that you've got 24v showing at the (+) stud on the voltmeter. I believe this wire is constant-hot and carries 24v at all times, so long as the batteries are connected. The voltmeter fuse is at the very bottom of the fuse block. Make sure this fuse isn't blown.
The other wire coming off the (-) stud of the voltmeter should connect to one of those two black relays that you've discovered. It should be the relay WITHOUT any brown wires connected to it. I believe the wire is black with a white stripe, but I can't confirm... When the key is turned to the "on/run" position, the relay will close with a firm 'click', the black/white wire connects to ground, and the voltmeter should come to life.
If the voltmeter relay is not closing when the key is turned to "on/run", then either:
- the pink wire with a black stripe is not supplying the relay with ignition-hot 12v
- or the ground circuit to the relay is open and not connected to ground
- or the relay is defective
