I've had a 2005 CAT 247b for a little over a year. It has 1050hrs and is in good shape overall. It was running fine, then parked for 2 weeks and won't start. Turn the key and no lights come on, hour meter goes blank, no crank Tried jumping with cables Replaced battery with new AGM Cleaned battery cables and checked for loose connections Checked for blown fuses, haven't found any. Replaced ignition and safety switch on bar in cab - no change Have 12.5v between battery posts Have 12.5v to starter, main breaker and positive jumper post near relays/main breaker with key off Have 3-5v to starter, main breaker and positive jumper post with key on Sometimes the dash lights will come on with the key and it will get 12.5v everywhere until I go to start it. Then the dash will go blank and the voltage will drop back to 3-5v when checked. The starter will only click once, no crank. Any recommendations? I'm at a loss.
Do you have 12.5 from battery hot to frame? Take apart all grounds and clean. A bad ground can pass the micro current that will allow a volt meter will read as 12.5 but when you try a much higher amperage it won’t go.
That would appear to be the root of the issue. Is the 3-5V is measured at the incoming or outgoing side of the main breaker.? Simply turning the key from off to on should not do that. I wonder if there is a relay sticking somewhere.? Do you have the electrical schematic for it..? If not post the S/N and you can have a copy.
Thanks for the suggestions. I removed, cleaned and reinstalled the main ground to the starter and the three ground straps I could find. I have 12.5v from the frame/block to positive terminal of battery when key is off. Now I only have 1v when the key is on. I will get one new relay and try swapping it out with the existing ones to see if that fixes it. I got the same voltage on both sides of the main breaker (12.5v key on, 1v key off). I do have a schematic that CAT Service emailed me. I just don't know what to look for when I have the same voltage everywhere.
Update. I replaced both battery cables and it started. Both old cables looked fine and didn't show any resistance issues with a multi meter. Thanks for the help guys.