Farmall 400 no charge

Joebanana

New User
I working on McCormick farmall 400. 12 volt positive ground. First a picture of a wiring diagram would be helpful and 2nd could some tell me how to diagnose a no charge condition. Originally the volt guage just sat in middle and did not move. Then ignition switch accidentally touched frame of dashboard when I had it out. Shorted to ground and I assume that's when guage now reads all the way to left. Starts and runs still but guage doesn't move, lights work. Any help greatly appreciated
 
Welcome Joebanana!

First, need a little more information, is this a diesel with a 12v generator, or gas with 12v conversion and an alternator?

As for the meter that stays all the way to the left, is that possibly an amp meter instead of a volt meter? If so, possibly it got hyper extended from the short, and is now just jammed in that position. If it never moved before, it was probably not working before it got shorted to ground. An amp meter actually measures the direction of current flow, not voltage. Being there is still power to the ignition switch, it still starts and runs,the meter is not the problem, it is just not reading as it should.

To diagnose the charging system, you need a volt meter. Check the voltage across the battery, engine running up to +1500 RPM, The voltage should be around 13.5v for a generator, around 14.5v for an alternator. If the voltage is down around 11.5 to 12v, it is not charging.

Check the voltage, answer back if it's a generator or alternator, look at the gauge carefully, see if it's an amp meter or volt meter, let us know...
 
Probably an amp (rather than volt) gauge. (I'm not totally familiar with the 400s gauges) If an amp gauge, then sitting in the "middle" would be normal with the engine not running. An easy check to diagnose charge or no charge conditions is measure the voltage at the battery terminals with engine running. Approx 12 volts means no charge - approx 14 volts means system is charging. Post back and others will no doubt chime in with more details.
 
Do a search for Bob M Farmall Diagrams

Since it is positive ground I assume it is a generator with external regulator and not a alternator

If gauge rested in the center at 0 it is an amp gauge not a volt gauge. If battery is well charged and engine starts good the amp gauge will not show much movement.

Gauge all the way left could just be a stuck needle. Take the handle of a screwdriver and gently tap the gauge and see if it will free it. If not will need to replace the gauge. If it starts and lights work the gauge is not cause of no charge.

Check voltage at battery. Should be about 12.6 volts at rest and 13 to 14 running at half throttle or more.

If voltage does not rise when running, ground the Field post on generator. If it now charges you have a bad regulator side in the voltage regulator. If it still does not charge leave field grounded and jumper from generator armature or armature tab on regulator to BAT on regulator. If it now charges you have a bad cut out side in the regulator. If still no charge check for generator or wiring problem.
 
Thanks all
When I get a chance to get back to it will check what was suggested. Probably right, misstated as volt guage, but is more than likely amp guage. Battery appears to be 12 volt and is newer August of 2017. Doesnt say maintenance free so popped off two covers and water was up and had six fill holes. Appears to be a generator, two wires coming off the top. I believe one was blue and one was yellow. Also appears to have voltage regulator on left side of tractor when sitting on it. Between dash and starter. Didn't have multimeter with me but will check charge status when get back to it.
Thanks again
Joe
 

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