1958 720 D pony, 6 volt not charging....

~"When I turn the lights on the amp meter is pegged in the discharge position"..answer--that is also normal if the diesel isn't running. With the diesel running that's not normal & you then have a charging problem.

~ The red light above the fuel gage does not light up..answer--that could be normal, depends on the pony oil pressure. Or your S/N range 720D tractor that light only lights when the pony ign switch is on & the pony isn't running, or the pony doesn't have oil pressure. If the light isn't illuminated with the pony ign switch on & the pony not running, make sure the light pigtail is attached to the oil pressure switch, if it is, then suspect a burnt out bulb. The lens doesn't come off, the light socket pulls out from the rear..[good luck unless you have 5 elbow joints & small hands].

~Now on to test that 6 volt diesel generator.....First, make sure you have battery power [6 volts] at the {BAT} terminal on the regulator, if not find out why [it gets it's power from the non-battery side of the ammeter,,,then make darn sure the regulator base is cleanly grounded to the generator,,,then momentarily touch a jumper wire from the {BAT} terminal on the regulator to the {A} post [larger of the two] on the generator, if it sparks that will properly polarize the generator. If you don't get a spark you either have a bad field relay in the regulator or an open in the generator field, or open wire between the two. If no spark, ground the {F} post [smaller of the two] to the generator case, then re-touch that jumper wire from the regulator {BAT} terminal to the generator {A} post, if you get a spark then you could still have a failed regulator, or an open in the wire from the generator {F} post to the regulator {Fld} terminal. If you do get a spark move on to a running generator test.

~Running test...With the engine running at fast idle short the generator {F} post to the generator case, does it charge now? If so you have a bad regulator, or open in the wire from the generator {F} post to the regulator {Fld} terminal.....If still no charge leave the {F} post grounded & run a jumper wire from the generator {A} post to the regulator {BAT} terminal, does it charge now? If so you have a bad regulator or open in the wire between the generator {A} post & the regulator {Gen} terminal....If still no charge re-check for battery power at the regulator {BAT} terminal.

~If it appears that your generator isn't functioning, pull it apart & clean the brushes & brush holders, check for broken brush springs, & clean the commutator of oxidation. While in there look for broken, burnt, or shorted wires..

~For some reason on those late Diesels I seem to find the fuel gage wire on the wrong regulator terminal. I don't know for sure but suspect an incorrect wire diagram out there somewhere. Make sure the fuel gage wire in on the {Gen} terminal & not the {F} terminal .

~It helps if you print this check list out & take out to the tractor with you....

~Any questions just post back.....

Assuming all other simple things like an open or shorted wire or open circuit or bad ground connection or loose belt or a plain old bad battery are NOT the problems of non charging, try the below:

To troubleshoot whether the VR is bad, first be sure the belt is good and tight and the generator has a good ground to the tractors frame and that the VR has a good ground to the generator. With the tractor running, use a jumper wire and connect the F post out of the generator (smaller of the 2 gen posts) to the generators steel frame ground, and if the ammeter then shows charge, you either have a bad VR or a bad/broken wire connection between the generators F post and the F terminal on the VR.

If she still doesnt show charge, leave the F grounded, and then momentarily conenct the BAT and ARM (or GEN) on the VR together to see if it shows charge. If she charges then, you have a bad cutout relay inside the VR.

With the F still grounded and the GEN or ARM on the VR connected to the BAT terminal and if the Gen and VR have good grounds and assuming the BAT terminal is connected to the battery via the ammeter and she still dont charge, its probably a bad generator.

You can also motor test the gen by removing its belt and all its wiring (protect all the wiring so it doesnt short out) and jump wiring the ungrounded bat terminal (i.e. - on a + ground system) to the generators ARM post (larger of 2) and the generator should turn like a motor. A source of such battery power could be the wire from the VR's BAT terminal, as it leads to the battery via the ammeter. If it runs when you do that, then ground out the generators F post and she should slow down slightly. If not, the gens field may be bad. If the gen turns when you apply battery voltage (from the BAT lead or elsewhere) and slows slightly if you ground out the F post, it should generate power fine.

For the generator to charge the battery, there has to be a connection between the BAT terminal on the VR to the battery (usually via the ammeter) and test that by using a test light or DC voltmeter and battery voltage should be present on that post ALL THE TIME. If the gens power doesnt reach the battery, it cant ever charge it, and the path is out the ARM post on the Gen, to the GEN or ARM terminal on the VR, through the VR's cut out relay, out to the BAT terminal on the VR, through the ammeter, then to the battery.

If she dont charge despite all that and the tests show the gen is bad and NOT the VR because you by passed BOTH the Field and Cutout Relay per the tests above, and the rest of the wiring is good and the gen and VR are grounded properly, heres a few gen troubleshooting tips:

Many problems are the brush hold down spring assemblys are rusted and corroded so the brushes are not held down tight against the commutator. Use a wire brush and WD 40 and air etc to clean and free up the hold down spring assemblys so the brushes are held tightly down. If the brushes are not worn down too low and held down tight and she still wont charge, you may have an open field winding or a bad armature or a commutator problem. Post back if you want to repair the generator and maybe I can provide more tips.

I assume you have tried to polarize the generator lately???

Since the ammeter seesm to be working from what you said, the VR's BAT terminal still has to get to the battery to charge it, and thats usually connected to the load (opposite battery side) side of the ammeter. However, if the VR's BAT terminal shows battery voltage, that shouldnt be the problem.

If the gen is charging and VR working at wide open throttle (even if ammeter happens to be bad but not open) the battery voltage should rise from 6.3 volts to around 7 and the lights should glow brighter.

I hope this helps you troubleshoot whether its a bad gen or VR, so post back any questions. Dont overlook a bad ground or a missing connection per the above.

God Bless the USA and please pray for our troops.

Ol John T Nordhoff in Indiana