Electrial problem on 5 ton dump - M51

[poppop]

Electrical problems make my head hurt so I hope someone can lead me in the right direction to find this problem. The truck has sat unused for about 6 months. When I went to get it there was no power when the master switch was turned on. OK, batteries are old so must be dead. Charged batteries and they tested good, reinstalled and same thing, no power. We can jump starter and it spins fine. I pulled the master switch and one wire was badly rotted and broke when I moved the switch. I repaired that and still no joy. I confirmed I have two hots coming to the switch and confirmed the switch is good, so two hots leaving the switch. My question is where does the power go when it leaves the switch??? Does power go from the switch to the breakers or from the breakers to the switch?? What sends power to the gauges?? I hope someone can give me some pointers.

 

[MtnSnow]

Likely your PCB (Power Control Box) is need of replacement or a rebuild with the master switch testing out good. It is located on the drivers side firewall just next to the Washer fluid bottle.

 

[poppop]

I probably should have said this is an older truck, an M52 I think. I did see a silver colored metal box with fins on it mounted on the firewall. It has a large bundle of wires with a screw plug connected to it. I assumed that was a voltage regulator.

 

[11Echo]

I probably should have said this is an older truck, an M52 I think. I did see a silver colored metal box with fins on it mounted on the firewall. It has a large bundle of wires with a screw plug connected to it. I assumed that was a voltage regulator.

M52 is a tractor, M51 is a dump truck.