Ammeter pegged fully left

Farmaller63

New User
Got my '42 M out today to give all the kiddos a ride on Easter. Tractor ran great as always and everything was working perfect when I got her out. I shut her down in the yard to visit with family some more, thinking I would just put back in the barn a little later. When I went to put her back in the barn, I started her up and noticed that the ammeter was pegged completely to the left (discharge). I switched the charge/light selector to all settings (L,H,D,B) with no result - just stayed pegged to the left. Checked the lights to find that none of them are now working either. I shut her down and the ammeter stayed pegged to the left. Started her back up to see if the ammeter would return to center, but it did not. Not sure what's up with this. Never seen this before. Any thoughts???
 
Something probably shorted and flopped the ammeter to full discharge, then burned it out and it stuck there.

If that's NOT the case, it's sitting there right now with a big drain on the battery, possibly though a stuck cutout and the generator, killing the battery and trying to start a fire from hot wiring and whatever component(s) are involved.
 
It reminds me of something that was grounded, becoming not grounded. I've had corrosion and rust and dirt cause some grounded items on my "H" to get non-grounded. Soon as I figured it, it got fixed.
 
It is either a failed gauge, or your battery will be dead soon.

Take a lead off the battery, if gauge stays over or no spark, bad gauge.
 
No, starter is not stuck and, after about 5 hours since I noticed this, the batt is still strong and appears to be fully charged. Disconnected the batt until I can diagnose more tomorrow.
 
i bet the regulator contacts are stuck closed. just tap the reg. and they should open. i have experienced this.
when tractor is started they close and charge, then when switch is turned off the contacts should open.
 
That sounds like a stuck ammeter. Did the ammeter needle stay fully left after the battery was disconnected? If yes then it is indeed stuck.

Sometimes the needle can be freed by bringing a strong magnet to the glass front then moving it around. Otherwise the only fix is to replace the ammeter.
 
Did the ammeter stay stuck to the left when you removed the battery cable?

It's physically impossible for the ammeter to be reading any sort of current with the battery disconnected and the tractor shut off. That means if it still shows stuck to the left, it is toast.

If the ammeter were reading an actual current, you would have smelled, and probably seen, smoke very quickly. None of the wiring past the starter on that tractor is designed to handle 20++ Amps of current for very long.
 
Barnyard... I totally concur with your prognosis. I think the ammeter is likely shot because it does stay pegged to the discharge side even when the tractor is
off and the batt is disconnected. Now I just have to figure out what may have caused this to happen. The ammeter was brand new, just installed about 4 weeks ago. Any thoughts on where to start tracing circuits is greatly appreciated.
 
I'm going with the ammeter is mechanically STUCK (also maybe now open) plus maybe a sticking cutout relay ??

In the event the cutout relay contacts welded closed, there would be a high current discharging the battery through the generator, the genny would get hot, and the battery discharge BUT FROM WHAT YOU SAY (battery okay) and the genny isn't getting hot and there's no smoke,,,, THAT DONT SOUND LIKE THE CASE.

UNLESS THE AMMETER BECAME AN OPEN CIRCUIT !!!!!!!!!!!!!!!!!!! it should read very low resistance through it. Use an ohm meter or a continuity checker, remove all the leads, and insure the ammeter is still a low resistance pass through device ?????

Sometimes light tapping or a strong magnet like Bob M noted might let the ammeter return to center, but its important it still has continuity through it and all can still work even if the needle is stuck other then it wont register correctly. CHECK AMMETER CONTINUITY !!!!!!!!

As far as what happened, if the cutout relay sticks closed on shut down there will be a fairly high discharge current and it could cause the needle to stick in full - discharge, but if the relay stayed stuck closed the battery would have ran down fairly fast (and genny get hot and maybe some smoke??) BUT MAYBE THE CUTOUT REALY UNSTUCK AND OPENED BACK UP so the battery didn't discharge but the ammeter is just mechanically stuck

CHECK AND KEEP AN EYE ON THE CUTOUT RELAY AS IT MAY STICK AGAIN AND INSURE AMMETER STILL HAS PASS THROUGH CONTINUITY (so can still charge even with stuck needle) You may need a new ammeter and have a faulty cutout relay ????????

John T
 
John T.

When I took the hood off to look at the voltage regulator, I noticed the wire connected to the BAT post on the regulator had a bare spot just beyond the connection point. Looked at the inside of the hood and found a similar spot. Looks like the BAT wire coming from the ammeter was rubbing up against the hood and eventually arc'd (probably several times in a row). Went back to the ammeter to check the continuity as you suggested and found that it was reading no continuity at all... It's fried. Had another new ammeter in my shop waiting to put on the '48 Super A that I am currently working on, so I put that on the M. All good now. Thanks a million for your help in diagnosing, as well as everyone else who replied. Sure appreciate you guys and your willingness to chime in and help with problem issues. Have a great week!
 

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