I have a 277B cat skid steer model number BHMD00251. I am having a problem with the electric system. I was going up the drive loss of power and the machine quit an would not start with the key so I jumped cross the starter it started .But would not move I reached up an turn on the dome light on And it killed the motor the controls do not work.
You have a loss of ground on the controls side, trying to make ground back thru the harness. Could be a bad connector, greened up wiring, some wiring buried in belly pan muck corroded to hell and gone, will need to hand over hand the harness to find this kind of catastrophe.
If you have 12 volts at the battery then you must have a poor cable connection between the starter where the accessory power supply wires comes off and the main power supply terminals. You could also have a bad cab ground. Lift the cab and check the ground strap at the back of cab.
I will start with checking the batteries first, I did lift the cab and check the ground cable cleaned it up and put back together Will keep watching for other responses