Komatsu PC120-6 won't start. Even tho key is switched off, display stays lit up. Could the battery relay be defective? Internally shorted together that it transmits a surface voltage, but not well enough to run starter? I'm not at the machine.. Thanks
Try disconnecting the "R" terminal wire from the alternator, then see if the engine will start.
Does this machine have the Cummins clone engine?
I'll find out. I think so. Would that mean there's a different voltage supply schematic?
It might. I seem to recall some machines used an external diode for the Cummins clones instead of the R terminal on the alternator. Another check is watch the monitor panel when you turn the key on a see of the low oil pressure alarm comes on. If so there is voltage bleeding through the diode in the alternator. This tells the computer the engine is running but no oil pressure on that sensor says you should shut down the engine that isn't running. Make sense