Sometimes I crank the backhoe and the battery indicator stays on and the hour meter stops working. A quick off and back on with the ignition switch will often rectify the problem. Jiggling or playing with the ignition switch does nothing. The W wire from the alternator feeds these items and even when the battery light is on, I still get a AC sine wave from the W wire at the alternator. I noticed that part of what this W wire feeds is a "Pulse Detection Circuit". Anybody familiar with that? Could that be causing this intermittent problem?
The pulse detection circuit is what controls the alternator light. It looks for the alternating current and then shuts off the ground to the light when charging. If it does not see the alternating current then it grounds the light and the light illuminates. It is part of the monitor and not replaceable. I guess some type of internal short could cause your issue. Did you check for AC voltage (approx 7.6 V AC) at the monitor P6 terminal when the light is on?
Thanks mg. Where is that P6 terminal and I will check for it there?
I have a JD that will do that, for me the tach usually turns on after a minute or so, sometimes after revving a little. If I remember, the alternator is not charging during that time. So I'd look at the alternator power feed and the alternator itself. I've never looked into it more because it's never been a big enough issue, and I didn't have MG to ask about it either.
If you rev it up like Delmer says and it works then it is an excitation issue. That would be the wiring to the D+ terminal on the alternator. For checking AC at the monitor it is Pin 12 on the monitor connector (M39 purple wire).
After some troubleshooting, I do believe it is excitation (idle speed) related. I plan to rework/clean the D+ connection and the W wire connections. I do have a habit of cranking the tractor at low idle sometimes and that may not be kicking off the alternator. Thank you.