well our machine burns I guess 3 times a yr it seems. An it's always in the same spot. At the battery disconnect switch. (The giant disconnect relay). Well I've patched I guess 8 differ times over last few yrs. well this time there wasn't any thing left of the harness. So we ordered an replaced the harness from Cab to disconnect relay An from that harness to starter safety relay mounted on starter. Well now my machine is still dead in the water. Want start from the key, so I jumped the starter An cranked it up an it want drive. I have the service manual down loaded to my lap top from our local komatsu dealor. I tell ya there information on there older machines that's on PDF files is a pain in the rear to go threw for trouble shooting. Not to mention there's not a wireing schematic on there. I've asked them to print me a schematic an they said it's just as useful as PDF files. As of now I have. New key start switch ordered an another short wireing harness to hook into the new harness that's to tie into disconnect relay. (I had to make a jumper to it to get power to fuses). So I'm Asking is there any one out there that has any experience with one of these old dinosaurs . Love to find a schematic that's color coded An tells Me what's hot an when like cat schematics do. I'm Guessing with all the reading I've done bout the starting An stoping of the motor is all tied in with the safety start relay that's mounted to starter An tied in with shifter lever too to complete a ground circuit . Thx for Any advice guys
There should be a bunch of relays behind the seat in the cab that you will need to check. There are also diodes in the wiring harnesses in different places in the machine. Have you checked all the fuses in the panels. Does the monitor panel show a low engine oil pressure alarm when you turn the key on but the engine isn't running. If so you have a diode blown in the alternator. There should be an extra wiring that is a small diameter going into the harness. If so disconnect it and tape it up so it doesn't touch anything. If the engine will start now then you have a problem in the alternator. The other bad things about these machines was that the insulation on the wires will go bad over time and you will get shorts that we used to call cross talking. Komatsu was pretty proud of their electrical systems. Most of the people who had to fix them hated working on them but loved the overtime it usually took to find and fix the problems. The schematics are what they are. You will not find any real good ones from Komatsu. If you work on the brand long enough they do become easier to understand.
Had replaced the main harness from Joystick to engine compartment. Then replaced the short harness off that one to the start safety relay that's mounted on starter. Then found out that there was another short harness that ties into the new main harness An hooks into the master shut off service relay. Am to answer ur question bout the monitor. Nooo. I've been here 8 yrs an it's never worked nor has the machine ever had brakes nor does it build air press either So there fore I haven't a clues off how it's operated all these yrs with out air press to over ride the low air press eletric brake under the floor at the brake pedal valve. Some how it's worked all these yrs with all these electrical bugs. I'm scared once all new wireing is complete then it sure nuff want drive due to no air pressure to work brake electrical switches.