PC35 MR-2 Komatsu excavator. Machine was sitting by my garage while rebuilding the stick, replacing all bushings and replacing leaking hoses. Having to move the machine a few times while working on things I had an issue where the starter would not turn over the engine, just acted hung up. Removed starter, bench tested it and found it was working OK, little sluggish and worn. Installed it back, still same issue where solenoid would not engage or even click. Checked power from batteries, good Checked power to starter, good Checked power to kicker wire with Key held to start, No voltage ah we have a problem. Mosquitos were bad that evening so I went back out later that night checking fuses and relays with no issue found. Tried key one more time and machine cranked right up. Next day back to No start. Pulled starter again and checked it on the bench holding power a bit longer and it started to slug down quick. Brought to repair shop, told it was worn out as I knew, Parts not readily available so I bought a new one that came in two days later. Installed new starter, all is well and machine got put to work in the yard. Three days ago working machine half day, took a break to eat and refuel machine, Same no start no click no nothing when key gets to start position. Removed panel cover to get to key switch wires, they looked dirty and had some corrosion from time. Cleaned each wire terminal and lug on the key switch, cleaned all other electrical connections in the area. Connected batteries and machine started right up, fixed issue as I thought. This morning got another couple loads of fill to the house, worked machine, needed more fill and when I got back with another load of fill I tried to start the machine and same issue appeared. No power to the kicker wire on the starter solenoid. I did notice the shut off solenoid on the injection pump is / was hot to the touch when the engine was cool from not running for 2 plus hours between me getting more fill. I do not have wire schematics for this machine so I am going off of intuition and past experience checking possible causes, Open to suggestions as to where / what to check next.
Canopy machine No cab.
Got worked through some tech info and schematics then got to testing. Found the issue was corrosion deep inside the three wire alternator plug, cleaned that off / out and was able to repeat the issue over and over again. Diode in the alternator was bad, had more than one volt with machine off going to the computer. Removed single wire and machine started right up. Ordered new alternator, installed and not had the issue since. With the corrosion in the three wire plug I could not get a proper test or diagnosis. Plus this corrosion would keep the machine working properly sometimes and sometimes not.
Shout out to you @John C. I appreciate your help, generosity