generator

My 39a isnt charging the system. It has a gen (with a cutout i think), lights, starter and a switch. Starting from all the way on the left, there are 3 more detents on the switch, is this a 4 or 3 position switch? The next question is how can i tell if the gen is outputting simply? can i read with a ohm meter at the gen? if so which contacts? The wiring is new and known to be proper but i dont know if the switch, relay or gen are to blame. Thanks in advance!

Couple of first points. What you have is a four position switch. The very counter-clockwise position is for a low charge rate (no lights). The next three positions going clockwise are all a high charge rate, the first one being with no lights, followed by dim and then bright lights. This switch is used with a cutout relay (as opposed to a voltage regulator) and was quite common.

I don't have it bookmarked (I should) or I'd just give you the link, but if you search the archives for John T's troubleshooting guide for charging systems, it's an excellent step-by-step walk-through of making sure things are in order and isolating/identifying any problems.

With any luck he or one of the others will jump in and post the link.

Here's the link
John Ts Most excellent troubleshooting guide for charging systems

Great thanks! Thanks for settn me strait about the radiator too

Yer welcome! With any luck, you'll find that all you need to do is polarize the generator, which is a good possibility if it's been sitting idle for a long time.

Let us know how you're makin' out. John T and a couple of other very capable electrical types hang around here quite a bit and can help you if things arent' making sense or you hit something you can't puzzle out.

Scotty gave you the link to my long winded but complete test procedure, but heres short answers to your direct questions:

The next question is how can i tell if the gen is outputting simply?

Place a voltmeter on the battery, if its a 6 volt battery it should read around 6.3 volts (twice that if a 12 volt) just setting there tractor not running,,,,,,,,then when she is runnign at fast RPM IFFFFFFFF the charging system is working,,the battery voltage should rise to the 6.5 to 7 or a lil over range (twice that on a 12 volt system) ..If it never increases battery voltage, shes likely NOT charging..

can i read with a ohm meter at the gen?

NO you need a voltmeter

if so which contacts?

The gennys output is measured from its ARM post to case ground


The wiring is new and known to be proper but i dont know if the switch, relay or gen are to blame.

See Para 5 of my Troubleshooting Procedure to see if non charging is a generator versus a regulator or light switch type of a problem.

If you jump the gennys FLD post direct to case ground she ought to max charge so when shes running at fast RPM momentarily short the gennys FLD post to case ground n see if she charges then (ie see if battery voltage rises and/or ammeter shows good + charge). If so but NOT otherwise, the genny is okay so the problems in the light switch or its not grounded or the wires open from FLD on genny up to light switch........ If dead grounding the FLD post dont make her charge, leave it grounded when shes running and temporarily by pass jump around the cutout relay by connectign its BAT terminal over to its ARM/GEN terminal n see if she charges then????? If so but NOT otherwise the cutout realy is bad or not well grounded. If theres still no charge with FLD dead grounded and the cutout relay by pass jumped, sounds like the genny isnt charging

Check my procedure that Scotty posted for more detail

John T

From reading your posts, you seem to be new to this.

Just some friendly advice if you don't already know.
The Farmall A was originally 6 VOLT POSITIVE ground which confuses many newcomers that are used to 12 V negative ground. What it is now is anyones guess but it will work either way if the gen is polarized correctly.

John T made a remark about grounding that jumped out at me. That 4-position switch needs to be grounded through its body, i.e., where it mounts to the front of the panel and then the panel to the frame, through the box itself.

Have you painted the tractor? If so, did you paint it so thoroughly that you wound up with a poor ground for the switch? With everything mounted in place, a quick test with an ohmmeter between the male thread of the switch where it pokes out the front of the panel and a known good ground or the grounded post of your battery should show little to no resistance. Places where paint might interfere are: between the switch body and the panel/face, between the panel and the box, between the box and the stud that holds it to the steering support, and the two long screws that hold the panel/face to the box.

One of those devilish little things you could chase circles around for days.