JD 4020 24V system help!!!

GCHIRSCH

New User
I'm restoring a 1965 4020 Diesel w/ the 24V system (first tractor I've done, so please be patient.) Tractor was pretty rough. Engine is done. Working through the 24V system. Got the start system to crank and charge the battery. Working on the lights now. I keep getting 24V to the lights. When I try to hook the ground wire to the frame on the cable between the two batteries to get 12V volts to the lights, I'm getting a large arc. Any suggestions what I'm doing wrong? Read some other forums and they said the 24v system is insolated from the rest of the tractor. I don't under stand how I can hot a wire going between the + and - post to the frame and not get an arc.
Thank you
Greg
 
The common point between the two batteries IS supposed to be connected to the chassis, basically creating a 12 Volt (+) grounded system to half the lights and a (-) grounded 12 Volt system to the other half of the lights.

The generator, voltage regulator, and starter solenoid and starter are the only components that "see" 24 Volts, the fuel gauge and lighting loads "see" 12 Volts.

I've got a reply down another guy down on the DEERE Forum, and I'll cut and past a segment here...

"If you have an older model, there is a battery cable from the (+) terminal of the LH battery to the chassis, and a battery ground cable from the(-) terminal of the RH battery to chassis ground.

If it's been updated (for safety) or is above #90999, there's a common cable from the (+) terminal on the LH battery to the (-) terminal on the RH battery, and a slow-blow fuse in a jumper wire (or a length of fusible link wire) from that common connection to chassis ground.

If you have that system, with the crossover wire, that connection to the chassis MUST be present and intact for the lights, indicators and fuel gauge to function properly.

The (-) cable from the LH battery connects to the upper large terminal on the starter solenoid, from there a blue wire makes it's way through a circuit breaker (if new enough or updated) to the key switch and on to the light switch through some wiring harness connectors and a circuit breaker on the tip out steering pedestal panel... you should be "seeing" (-) 12 Volts (nominal) with respect to the chassis, on that blue wire both at the key switch and the light switch.

The (+) cable from the LH battery connects to the terminal on the starter "belly" facing the engine block, from there a brown wire makes it's way through a circuit breaker (if new enough or updated) to the key switch and on to the light switch through some wiring harness connectors and a circuit breaker on the tip out steering pedestal panel... you should be "seeing" (+) 12 Volts (nominal) with respect to the chassis, on that brown wire both at the key switch and the light switch.

If power is missing at the blue or brown wire at the light switch you'll need to trace it back through he breaker(s)on the tip-out panel, the wiring harness connector in that area, on through another harness connector under the rear of the hood/front of the steering pedestal cover, on down to the starter, though the pair of breakers there (if new enough or updated for safety.

So, check for the midpoint grounding of the batteries, and for the (+) 12 and (-) 12 Volts at the switch panel and let us know what you find! "

As to the SPARK when connecting the ground at the midpoint of the two batteries, the innards of the stater solenoid, the starter, the voltage regulator, and the generator need to be totally ISOLATED from their housings, frames, "bellies", etc, as any direct contact between a (+) 12 Volt part or a (-) 12 Volt part will cause the issue you are having.

Could be something connected wrong in the wiring, an internal short to the case/housing/frame of the components previously mentioned, a even POSSIBLE someone has installed a 12 Volt starter, or solenoid, or regulator, or generator NOT built with the internal isolation this system DEMANDS.

What is the serial number, and does it still have a generator or has it been converted to an alternator system?
 
Thank s for the quick response.
My serial number is 104069, which indicates 24 volts.
When I bought the tractor they had the wrong starter on it and and an alternator that was not hooked up. I purchased rebuilt ones from a local starter repair shop.
When I check the voltage to out of the light switch to the frame, I get 24v. When I check it to the common wire, I get 12v. My common is not grounded due to the sparking. When I check the common to what should be ground, i get 12v.
Makes me wonder about your isolation comment. Is there a way to check the isolation of the starter, solenoid, regulator, and generator?
 

You're correct in that there should be no sparking when attaching the accessory ground wire from rear battery post to frame. Do your tractor batteries stay charged when engine isn't running?
 
(quoted from post at 07:41:17 03/12/18) Thank s for the quick response.
My serial number is 104069, which indicates 24 volts.
When I bought the tractor they had the wrong starter on it and and an alternator that was not hooked up. I purchased rebuilt ones from a local starter repair shop.
When I check the voltage to out of the light switch to the frame, I get 24v. When I check it to the common wire, I get 12v. My common is not grounded due to the sparking. When I check the common to what should be ground, i get 12v.
Makes me wonder about your isolation comment. Is there a way to check the isolation of the starter, solenoid, regulator, and generator?

From what you told Jim it HAS been converted to an alternator/ Was the proper "isolated" unit used? If it was an "off-the-shelf" 24 Volt unit made for a system that did NOT need an isolated case alternator it could well be the cause of the spark you are seeing at the mid point of the series batteries grounding wire.

You ask "Is there a way to check the isolation of the starter, solenoid, regulator, and generator?"

First thing we have to know, FOR SURE, does it have an internally-regulated alternator, or still the original generator with external regulator?

Basically, one would disconnect the batteries, then each individual component in question and check for conductivity (with an Ohmmeter) between it's (-) terminal and it's metal case, and it's (+) terminal and it's metal case.
 
Thank you Jim and Bob.
Sorry for the confusion. The tractor has the 24V system with a generator - no alternator. The previous owner did a pathetic attempt to change it over to 12V but nothing was ever hooked up. The started would not mesh with the flywheel, the alternator was just there to keep the belt on.
I went back to 24v to make it original. The harness was still in tact, so I used it.
I just rebuilt the engine and am working through the wiring system, so I unhook the batteries when I'm done messing with it for the day, so I cannot say if they are running down.
 

Nice to see someone with an eye for originality. The 12/24V system can be made to function but it is snooty and foul tempered.
There is a JD service manual with the wiring diagram. 1-800-522-7448 for the manual on CD or hard copy.
Jim at Agri-services builds an all new high quality electrical harness at a reasonable price. He even has a circuit breaker update that will reduce the chances of the tractor burning to the ground .
 

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