amp gauge

Farmall M positive ground. The generator was tested and is ok. VR is ok I think. What is strange is that when I turn the lights on with the engine NOT running the amp gauge shows discharge and does not return to centre when I turn the lights off. I have done all the tests that John T. reccommends to no avail. Could I have a bad amp gauge, and could it cause this problem? Ellis

Ellis - Sounds like the ammeter movement is sticking (it's not at all unusual).

Quick test: Touch a small magnet to the ammeter glass lens then move it around to deflect the gage hand either way from center. Now pull the magnet back away from the glass. If the pointer does not return to center the meter movement is sticky.

The only fix is to replace the ammeter.

Bob, I've been waiting all evening for a good tip. I'll try that 1st thing in the morning. Thanks, Ellis

Wayyyyyyyyyy back when I was a used tractor dealer it seems many/most older tractors amp gauges were rusted with sticking needles just as you described. However, so long as the gauge is still a continuous circuit as they usually were(an "ideal ammeter has ZERO resistance) just cuz the needle is mechanically stuck dont mean she cant still charge just fine. Put a voltmeter on the battery and when the tractors sittin there not running the voltage should be around 6.3/12.6 volts but when running at fast RPM IFFFFFFFF the charging system works voltage should rise to 6.5 to 7 on a 6 volt or 13 to 14 on a 12 volt. Additionally when you change from slow idle to fast RPM the lights should get noticeably brighter if shes charging.

If she dont seem to be charging (voltage isnt rising) see if it charges when running if you temporarily dead ground the gennys FLD post?? If so (means genny itself is okay) but she dont charge otherwise, the VR is bad or isnt well grounded or if it has the LHDB light switch (and cutout relay) its not well grounded or the wires bad from FLD on genny up to LHDB switch.

Sounds like you alreay tried my Troubleshooting Procedure, it should tell if non chargign is a genny versus the VR or other problem??

John T

I just had the same problem. Since the gauge showed discharge, even when taken completely off of the tractor, it was obvious I had nothing to lose by disassembling it. I carefully pried out the bezel lip all the way around the back of the gauge until I could remove it and the glass. After further disassembly, I found a tiny, tiny metal shard stuck to the magnet, causing it to hang up in its bracket. Removed the shard and reassembled. It works fine now.

sgtbull--- I am going to try that also. Ellis