MF135 charging system troubleshooting

Armymutt

Member
My 135 diesel frankentractor isn't charging. I replaced the alternator (external VR) and the VR with a solid-state type. Traced all the wires, checking for continuity. I'm getting about 13V across the battery terminals when it's running. I'm getting the same when I put the leads on the ground at the block and on the F terminal on the alternator. Looking at the diagram, I expected to get some sort of voltage across the oil pressure switch - I get none. Should I have voltage there? What else can I check? The ammeter is reading zero. I have no lights, so nothing to draw current once the engine is running.
 
Check the battery voltage when it is not running and then when it is running. A full charged battery should read 12.5 plus volts but not 13. If you get the 12.5 or so and the n13 when running good chance it is in fact charging just the amp gauge is bad. Also if your 100% sure it is not charging then the amp gauge could be bad and also cause a no charge condition. But if you have a bad amp gauge it can also cause a no run condition if it is an open gauge but if stuck in place can let ti still run
 
Did a few more checks. When I start it, the amp gauge swings in the positive direction. After that, it just sits in the middle. I discovered that the light for the temp gauge works. Not sure if it has enough draw to register on the amp gauge, but it isn't moving the needle. Battery voltage was 12.88 before I turned it on just now. When running, it was 12.65-12.7. After turning it off, battery voltage was 12.80. Any way of testing the amp gauge without pulling it out?
 
Well first off if all you have is the engine to pull amps things sound like they are working as they should and you have a very good battery since it shows a charge for a little while then little or no charge. To run the engine it out takes a few amps so the charging system does not have to work hard to keep the battery charged up simple as that. Sounds like the problem is all in your mind and you do not have a problem at all. I would stop trying to fix something that is not broken. Or if your that worried about it put some head light on it so the amp gauge will show a charge when you have the head lights on since they will pull l10 plus amps
 
OK. I hope this fixes it. I'd like to park the tractor someplace besides the driveway. Royal pain having to pull the battery every week when it's dead.
 
Well if the battery dies after sitting in a week you have a VR problem or some short or a short some place in the wiring. Easy way to figure that out is pull one battery cable and put a test light between the cable and the battery post. If it lights up you have a short some place be it in the VR or the wiring
 
You said you changed alternators to an internal regulated one. Did you use a one wire or three wire alternator? If it's a three wire unit you have to put a diode in the control line or it will feed power back even when turned off.
 
You best go back and read what he said!! He said he replaced it with an external VR alternator not an internal one
 
"[i:38bb97a132]I replaced the alternator (external VR) and the VR with a solid-state type[/i:38bb97a132]."

I took that to mean he switched to internal regulator. If not then i stand corrected.
 

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