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CaseFace, Mechanic
Category: Heavy Equipment
Satisfied Customers: 303
Experience:  22yrs Auto,Truck,Tractor Trailer,Heavy Equipment, Industrial Truck,Forklift,Motor Coach,Tour Bus
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John deere..we are getting 24 to our headlight and are blowing bulbs

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We have a 4020 john deere 24 volt system we are getting 24 to our headlight and are blowing bulbs we have changed the light switch and the key switch already any ideas
Has any wiring ever been altered at the batteries? just a quick look at a parts diagram it appears as though jd is drawing 12 volts for accessories off one battery, and 24v is only for the starter.
Customer: replied 8 years ago.
We put new battery`s and cables on it and checked grounds we also are having problem with the fuel gauge we have change the sender and the gauge we were told that they break the voltage at the light switch so thats why we change it we have always own this tractor from when it was new and this is the first problem we have ever had with the lights
did the problems start after you had changed the batteries? or did this begin prior to that? I see now how they split, one battery goes to the starter armature, the other to the starter solenoid, then some smaller, perhaps 10ga wires are going up to the switch
Customer: replied 8 years ago.
all this started before we changed anything the things we changed were all suggestion from the dealer and other mechanics
I will continue picking through the wiring diagram, I don't want you "throwing" anymore parts at it.. I'll be a lil while yet
Customer: replied 8 years ago.
thanks it hard to find anybody that wants to tackle 24 volt even our dealer

Ok, are familiar with voltage meters?

Customer: replied 8 years ago.

Next thing you will need ot do is check the wire on the starter housing, and, there will be a small wire coming off that going into the wiring harness, I believe brown. Then, up on the starter solenoid will be the other battery cable, and again, a feed wire coming off that, it should be blue in color and then goes into the harness as well. test voltages at those two points on the starter... Then , up at the light switch, you will find those two wires again, one on a terminal marked bat a and the other on a terminal marked bat b. I have a suspicion these two wires may be melted together in the harnes, in turn sending only 24v up to the switch. Let me know what you find..

Customer: replied 8 years ago.
sorry its taking so long, its an interesting system to figure out what may have gone wrong.. let me know what you find for voltages and the such
Customer: replied 8 years ago.
the brown wire we have 24 volts on it they are not melted together any were we took the harness apart the blue wire comes off the relay buy the starter and goes up to the light switch and we don`t have and juice there when the tractor is not running we didn`t try with it runnung because we have everything on hook right now and thing else we sould check ot
Customer: replied 8 years ago.
we just got everything hooked back up we still don`t have and juice on the blue wire


Can you verify for me this connection at the batteries?

Also, if you have the capability, check your generator and voltage regulator to see if either one is shorting out internally

(do not replace either until confirming their conditions) If you don't have the capability, you will need to bring those components to a facility that does

Customer: replied 8 years ago.



I do think this one has escaped me at this point. I will unlock and open up to other experts.. perhaps with our exchange of information, they will see something i had missed.
On the back of your light switch look for the Black wire coming off of R1
and the Yellow wire coming off of HD1 they should take you to a resistor
block it looks like.

Looks like they run to the resistor in the same loom, if they melted together in that loom
there is your 24v., or somehow at the resister.

That is from one diagram that I have, I have one other to look at and will answer again if
there is any difference.
Customer: replied 8 years ago.
I think your looking at the wrong wiring system our tractor is above 91000 that one does not use that resister we have been checking voltage should we have 24 volt at the key switch. We have 24 volt to the brown wire on the key switch when we turn the key switch on we have 24 volt on the brown wire on the light switch bat b. Any other ideas THANKS

Are the headlights on the fenders, and do you have 24 volt starter?

We'll get the problem solved.

Customer: replied 8 years ago.
The headlights are in the front of the fenders and yes it is a 24volt starter
Give me the wire colors on the light switch at:
1) R2
2) HD1
3) TL

Is the rear light working?

Yes you are supposed to have 24 at the light switch.

Customer: replied 8 years ago.
we don`t have a r2 we have r that has green on it hd1 is yellow we have a tl-1 and that is red we also have have a tl2 but there is no wire on that one
I am waiting on another diagram, I'll get back back as soon as i can.

I didn't get the diagram but I figured out what there doing with this

Do this:
The way you checked the brown wire and bat b on the light switch
your going to do just the opposite with your voltmeter.

Take the red lead and put it on the frame or wherever you were putting the black
lead on to test the brown wire and bat b.

Turn the key on and turn the light switch on as though you were putting the lights on.
take the black lead and check R-green, HD1- yellow, tl1 is your rear light and Bat A

Those should all come up 12 volts, if they come up 24, we will backtrack.

Let me know.

I have to be offline and I will check in.
I think that you going to find 24 volts at those wires especially Bat A.
I'm thinking that your whole problem is internally in your starter, feeding
the 24 volts to the lights, the lights power comes directly from the starter.

I'm going to put up an image on what to do. Put the leads from the volt meter
how I have them, take off the Blue and White wires first.
Let me know what happens. Where it says Ground Tans it is suppossed to say Ground Trans

Customer: replied 8 years ago.
Ok here is what we have the green wire we have no voltage the blue (bat a) wire we have no voltage and the yellow wire we have 24 volt now if we take the yellow wire off the switch and put 12 volt to the wire our lights work fine
Be with you shortly
How did you check the wire, did you do the reverse way, the way I explained

Did you get the drawing I put up and do that check.

Customer: replied 8 years ago.
Yes went right off of what you said to do and we used the drawing
Do this:
Take the cable end off of the negative terminal on the battery that has
the negative cable going to the starter solenoid.

Take the blue wire off of the solenoid and put it on the negative post you
took the cable off of.

The lights should now work fine if you do that and we just eliminated a problem
with all of the other wiring.

Do that and let me know.

I will be back shortly have to run out for a little while.

Customer: replied 8 years ago.
when we do that we still don`t have any lights
Check the voltage on the battery on the 2 posts of the battery,
then check the voltage from the negative post on the battery and
where the positive cable bolts to the transmission.

I'm going to make up 2 more diagrams for just to make sure we are on the same

I'm going to make one diagram where you can use 2 wires and a headlight,
and I will make the another using a voltmeter.

Please don't take any offense to them it is just to make sure we seeing eye to eye.

I'll have them up on Saturday 6/13 in the morning.

Customer: replied 8 years ago.
I will not ever take any offenes to help sometimes simple things can be over looked thanks again

Ok I just made one diagram, too much to make two, you can use a voltmeter and just keep
the red lead clamped to the trans where the positive cable goes, Or you can use a test light with a long lead clamped to the trans where the cable is.

Or you can use a headlight like I use on equipment and trucks, I can just set it somewhere
where I can see it or just see the light, that way you just have one wire and don't have to fumble with the test light in small places and you can go anywhere without have to keep reclamping the test light, you can even attach a small poker on the end to poke through wires with.

Try using the headlight way I think it is the easiest.
You might have blown a circuit breaker, they are on the drawing, just move along with
the one wire to test each spot, one wire has to be clamped to the trans always you will see it, and the blue wire needs to be clamped to the neg post on the battery by itself, all you have to do is check what I have on there.

You'll want to have the key switch on also.

Let me know how far you get, this is just to get the lights working from where the power
source starts so we know there is no problem with the rest of the wiring.

I don't exactly know what time I'm going to be on this weekend and I don't
know if you be working on the equipment.

One thing I have is the system figured out and I do believe you starter is the problem.

What you have is 3 different electical systems.

One battery is for 12 volt negative ground.

The other battery is 12 volt positive ground.

Then there is 24 volt for the starter which is isolated, and what I mean by that
is say you have just a 12 volt battery on a bench and you hook up the headlight
to the battery, that would be isolated. This isolated system uses the two batteries
to get the 24 volts for starting

You are not supposed to have 24 volts to anything else but the starter when the key
is in the start position.

Where the negative cable mounts on the solenoid is not supposed to be grounded
and is being grounded because that is the only way to get 24 volts to the lights, I also
believe you were having other problems with your fuel gauge.

That is one of the reasons why I keep saying to leave that cable off when checking the

I thought I would run that past you, you may want to look into your options on another starter.

I don't know how critical this machine is so instead of me waiting I thought I would let you know sooner rather than later.

Still check on the lights and see if there is any blown breakers, you can still get them
working but you can't put the Blue and White wire back on the solenoid if you want to
start the machine.


I have to correct myself.
You can't leave the Blue wire off, that also goes to your voltage regulator.
I don't know if you have been using the machine the way it is but if you've
been smelling battery acid stink that it could also be over charging.

If you find blown breakers I would put newones on yet.

CaseFace, Mechanic
Category: Heavy Equipment
Satisfied Customers: 303
Experience: 22yrs Auto,Truck,Tractor Trailer,Heavy Equipment, Industrial Truck,Forklift,Motor Coach,Tour Bus
CaseFace and 2 other Heavy Equipment Specialists are ready to help you
Customer: replied 8 years ago.
I`m sorry it took so long to get back with you my computor crashed and i hurt my back and have to have surgery next week thanks for all your help i will have to get back to work on it when i`m up and going later again thanks for all your help