Have a 95 Hitachi EX400LC-3 that when you turn the ignition switch off the engine stops but the hour meter and the lights on the monitor panel stay lit. I can hear a relay click behind the seat when I turn the key to the off position and when this happens the mode select lights change. (I,L,E,P) The "I" light is initially lit when I turn off the key and then when the relay clicks it switches to the "P" light staying on while the key is off. If I switch the key back to the on position without starting the engine the "I" light goes back on. When I start the machine it starts up in the idle mode and everything works as normal. The auto idle light and the hydraulic temp light is also lit as well and the hour meter stays running. If I take one of the small wires off the battery disconnect relay in the box under the air cleaner the relay will disconnect and all the lights will turn off. When I hook the small wire back up on the battery disconnect switch the relay stays off and the lights on the monitor panel stay off. I was reading in my service manual that the "L" terminal on the alternator supplies power to the monitor controller after the engine starts, which energizes a transistor that turns on the load dump relay. From the way it looks in the book to me, the load dump relay supply the battery relay with power directly from the battery to keep the battery relay energized when the engine is running. When the key is switched off and the engine stops and the alternator is no longer making power the load dump relay will open and and let the battery relay open. My problem is after starting the engine and then turning the key off, the engine stops but the battery relay stays energized. If I unhook the three wire plug on the alternator the battery relay will open and all the lights on the monitor panel also turn off. Has anyone else seen a problem like this and know if it might be the alternator, the monitor controller or one of the relay under the seat? I have not tried switching around any of the relays yet to see if that would change the problem. Thought I would check with you all before I did anything. Let me know if you have any questions or want me to try anything else.
I had a similar problem with a jcb machine two years ago. First thing to check is alternator, mine was back feeding the dash keeping the hour clock,ect ticking away. Couldnt pin down the problem till we realised it wasnt charging properly so checking charging voltage and for any current in the charging light wire when the ignition is off would be my first port of call
I will check to see if the alternator is charging. The light for the alternator is not lit on the monitor panel.
Just throwing this out there. There is probably a diode for the alternator excitation wire that is bad.
You are right, the diode is in the alternator. The alt. will charge ok but when you shut of the engine if the diode leaks the load dump relay stays energized and keeps the battery disconnect connected.
Usually when this happens with the alternator there should be an oil pressure light coming on and an alarm as the computer sees charging from the leaking diode (therefore eng running) but low oil pressure as the engine is not running. There is a D3 diode that will hold the battery relay on when it is gone but no engine oil pressure alarms go off. It is behind the seat attached to the main cab harness toward the right rear of the cab. Tough to find and describe.
Here is a picture of the schematic.
Before I got a chance to check to see if the alternator was charging the batteries went dead since I left the machine running all day long with the air conditioner running. I did this so I didn't have to unplug the alt. wire to shut everything down each time I shut the machine off and the fact that it was 95 degrees outside so the cab was nice and comfortable each time I had to get in it. Funny how spoiled you become when you have air. After purchasing a brand new alternator for $1000.00 (ouch) and replacing it this morning the problem is solved and the machine shuts down like it should. Thanks for everyone's tips and help.