I have a Cat 304E2 (Serial ME4) that was running just fine in all aspects, started fine, ran strong, etc. It sat for a few months without the battery shut-off so the battery ran dead and needed to be replaced. That's done and powers back up (the Compass display and shows 12V on the display). When the key is cranked, I can hear a few relays click but no attempt at turn-over. If I put a meter back at the start motor, there is a solid 12.5V. I'm assuming the starter cranks because of a control signal as the voltage is always there on the + wire. On the Compass control panel, the first crank oddly it reboots the display. then on any subsequent crank attempts is flashes the glow plug indicator for a second, a relay click or two can be heard, but no turn-over attempt. Any tricks or issues when a newer Cat exc goes dead like this? Is it some security feature that isn't obvious and I need to do some trick after replacing the batter with a new one?
Look at your solenoid, you should have two larger threaded studs, one cable goes to the battery +, and the other terminal goes into the starter motor, right? then there should be small wire coming out of the wiring harness and connecting to a terminal very close to those two big ones, right? that's the "control signal". As long as it's not in gear and going to take off and run you over, you can use a "remote start switch" (or a screwdriver) to connect that terminal to the battery + and the starter motor should crank the engine over. If not, check the voltage while trying to crank, either with a helper turning the key, or a remote start switch. You might find that 12V goes away when you put a real load on it because of a loose connection.
Check all the grounds. Probably one near the battery. Clean it throughly. Most of the weird stuff like that I’ve seen ended up being a bad ground. Also might check the cables, might have a bad battery cable. A quick voltage drop test will find those.
Good call on grounds but don't think that's my problem this time - lots of very clean leads/posts currently. My last test at starter positive was 12.57V and that was using chassis as negative point (motor mount and one other unpainted spot). Looking at schematic from service manual now for relay and solenoid suggestion from Delmer. Right now, I only see a "Engine off" solenoid but a WH-12-GXL control wire comes off pin 4 of Starter Relay so right now I'm looking at the "remote start switch" off that relay pin 4.
The remote start switch I was talking about is just a momentary switch with two wires and alligator clips, to hook to the battery positive and the solenoid small control wire, to activate the starter instead of shorting the small terminal with a screwdriver. Start at the solenoid on the starter, you can work back deeper into the wiring diagram if the starter works, but you're not getting the signal to activate the starter solenoid. Divide the problem in half, then narrow it down further. The remote start switch tells you if the starter is working, checking voltage at that small solenoid terminal while trying to crank will also tell you if it's getting the signal or not.
Understood and thanks for deeper clarification for any others that find this post later. I laughed at screwdriver short but I wasn't going to do that specifically but also can't say I've never not done something like that.
Is there an emergency shut off switch, could be red toggle switch or a red pull knob that got kicked or pushed in by accident?
Yes, there is a disconnect switch on Cats but that is I believe a negative disconnect and you wouldn't get the Compass display powering up, relay clicks on key turn, or voltage back at the starter motor so my problem is a bit beyond just the manual off switch I'm afraid. I have someone coming out tomorrow to look at it as I did get some progress looking at the control V+ from the relay but not enough progress to get it to crank. I'll update for the archive when I have a cause/fix.