John Deere 420 Crawler fuse

Bookman

Member
I "fixed" the lights on my 1958 John Deere crawler. That is, I put in new bulbs and new wiring. Unfortunately, when I turn the lights on, the dash fuse blows. Must be a short somewhere. I am definitely a newby at this. Can anybody tell me how to trace down a ground or whatever else is wrong? Key in your answer slowly, because I am a slow reader/learning when it comes to electronics. Thanks in advance.
 
To narrow down the problem, connect a spare headlamp in place of the fuse and disconnect individual lamps and wiring one at a time.

When you find the short, the spare headlamp will dim, or go out completely.
 
Just curious but if turning on the lights blows the fuse, why would not the same thing happen with another light bulb? Just asking before I waste a spare bulb. Since it is a six volt system would using a 12 volt bulb or even a 110 bulb work?
 
A short will blow the fuse, but simply light a 6 Volt lamp connected in place of the fuse as it would normally light on six Volts.

NOT gonna hurt the "test" lamp.
 
(quoted from post at 19:58:49 05/11/20) A short will blow the fuse, but simply light a 6 Volt lamp connected in place of the fuse as it would normally light on six Volts.

NOT gonna hurt the "test" lamp.

Thanks much.
 
I did some tests but I am not sure what they are telling me.
1. Disconnected the front lights, and left rear light connected. Connected a test light to the fuse holder and the other end to the negative side of battery (crawler is six volt positive ground). Turn on switch and test light did not go on.
2. I ran the test light directly from the negative anode of the battery to the rear light with the wire from the light to the dash disconnected and the test light went on.
3. I ran the test light directly from the negative anode to the disconnected wire from the rear light (running back to the dash) and the test light did not go on.
4. I connected the front lights and connected the test light from the fuse holder to the negative anode and when I turned on the switch, the test light went on, even with the rear light connected. Ummm
Any thoughts?
 
(quoted from post at 16:59:43 05/15/20) If it were me, I would take the fuse out and hook the lamp across the fuse connectors.
CPeter

"If it were me, I would take the fuse out and hook the lamp across the fuse connectors."

That's what I suggested.

I give up.
 
I used a test light instead of a lamp. When I turned on the switch with either of the front lights connected, the test light lights up. I took both the lights apart but I do not see anything. I traced the wire from the front lights back to almost to the switch and did not see anything. I need to get my fat fingers in behind the dash and disconnect the tach so I get enough room to see the backside of the combination switch. Now suppose I could run a wire directly from the negative side of the battery to the front lights to test them....if that would not burn out a bulb. If they work, then I assume something in the wire or at the switch. Patience folks. Thanks
 

This may have been asked and answered but I don t see it. Are you using the type of light that has a small bulb and reflector or sealed beam bulbs? What are the bulb, or sealed beam, numbers you are using? The small bulb type lights can have issues with intermittent shorting of the pigtails in the bulb sockets. With the seal beams you need to be sure the routing of the wires doesn t cross in a manner that heating melts the insulation and they short together, or that the hot wire doesn t contact the housing.

What size/ part number fuse are you using? You said you ran new wires but you are just now trying to access the switch the wires hook to, so not all the wires are new it would seem. Where exactly did you run new wires? Did you follow the schematic when you did your wiring?

As for using a bulb in place of the fuse as "wore out" first suggested to you. The test bulb, or light in your case, will light anytime there is a path to ground through the light. This can be a short to ground in the wiring or through a functioning bulb at the end of the wire. To eliminate the grounding through the end bulbs, unhook/remove the bulbs at the end of the wires (prevent the disconnected wires from touching anything that could make a ground). Does your test light still light? If it does you have a short to ground in the wiring. If it does not light the wire is not shorted to ground. Now be aware that vibration of operating machines can cause intermittent shorts.
If you remove the bulbs, isolate the wires, and run the machine around with the light switch turned on, does the fuse blow? If it does, I would say it is wiring, if not it would indicate something in the light assemblies to me.

Just my thoughts
 
(quoted from post at 13:43:54 05/16/20)
This may have been asked and answered but I don t see it. Are you using the type of light that has a small bulb and reflector or sealed beam bulbs? What are the bulb, or sealed beam, numbers you are using? The small bulb type lights can have issues with intermittent shorting of the pigtails in the bulb sockets. With the seal beams you need to be sure the routing of the wires doesn t cross in a manner that heating melts the insulation and they short together, or that the hot wire doesn t contact the housing.

What size/ part number fuse are you using? You said you ran new wires but you are just now trying to access the switch the wires hook to, so not all the wires are new it would seem. Where exactly did you run new wires? Did you follow the schematic when you did your wiring?

As for using a bulb in place of the fuse as "wore out" first suggested to you. The test bulb, or light in your case, will light anytime there is a path to ground through the light. This can be a short to ground in the wiring or through a functioning bulb at the end of the wire. To eliminate the grounding through the end bulbs, unhook/remove the bulbs at the end of the wires (prevent the disconnected wires from touching anything that could make a ground). Does your test light still light? If it does you have a short to ground in the wiring. If it does not light the wire is not shorted to ground. Now be aware that vibration of operating machines can cause intermittent shorts.
If you remove the bulbs, isolate the wires, and run the machine around with the light switch turned on, does the fuse blow? If it does, I would say it is wiring, if not it would indicate something in the light assemblies to me.

Just my thoughts

Jim, When I have the lights plugged in, I get a light on my test light. When I unplug them (or disconnect them, I do not. They are the old style with a light bulb in them. I do not recall the numbers on them. I think I may have a 15 amp fuse. I was told by someone not to put in more than a 20 amp. Sounds from what you are saying that the problem is with the bulbs in the light. I will work on that a bit and get back with you. I have a couple other tractors with six volt lights, and I have had problems getting them to light but never blew a fuse. With a John Deere 420 Crawler, a blown fuse stops the engine. On my Farmalls and one Allis Chalmers it does not. I am getting good (with practice) and taking the lights on and off and taking them apart. Thanks.
 
The test light lit with the bulbs connected and not lit when the bulbs are unhooked should indicate there is no ground in the harness wiring; the bulbs are creating the ground path. The exception to that would be if there was a minor path to ground that gets worse when operating, but I wouldn't go down that road yet.

JD calls for that to be a 20 amp fuse. I would put a known 20 amp fuse in it, to be sure it is not just to small of a fuse you are using. Carefully inspect all the bulb sockets, pigtails and springs in the sockets. I have seen the springs break or get deformed then contact a pigtail and cause shorts, the insulating washer that holds the pigtail centered under the bulb break allowing things to get out of place and short, and missing insulation from pigtail wires cause shorts. Carefully check the terminal blocks where the power goes into the light housings and connects to the pigtail. Be sure the reflector or its grounding spring are not touching the power connection.

Since the fuse also provides power for the ignition through the combination switch a short in, or heavy draw on, the ignition wire could blow the fuse. If you have anything else hooked to that switch it could be contributing to your problem.
 
(quoted from post at 18:30:42 05/16/20) The test light lit with the bulbs connected and not lit when the bulbs are unhooked should indicate there is no ground in the harness wiring; the bulbs are creating the ground path. The exception to that would be if there was a minor path to ground that gets worse when operating, but I wouldn't go down that road yet.

JD calls for that to be a 20 amp fuse. I would put a known 20 amp fuse in it, to be sure it is not just to small of a fuse you are using. Carefully inspect all the bulb sockets, pigtails and springs in the sockets. I have seen the springs break or get deformed then contact a pigtail and cause shorts, the insulating washer that holds the pigtail centered under the bulb break allowing things to get out of place and short, and missing insulation from pigtail wires cause shorts. Carefully check the terminal blocks where the power goes into the light housings and connects to the pigtail. Be sure the reflector or its grounding spring are not touching the power connection.

Since the fuse also provides power for the ignition through the combination switch a short in, or heavy draw on, the ignition wire could blow the fuse. If you have anything else hooked to that switch it could be contributing to your problem.

Jim, I connected a wire directly from the battery to the two front lights, and they lite up just fine. So the lights are working fine. They are the lights with just bulbs in them and single wire.

Then I connected a wire directly from the battery to the rear light. It did not light up. It is a sealed beam light with two wires, with one being a ground. I ran a wire from the ground side to what I thought would be a good ground on the crawler. The light still did not lite up. However, when I ran a ground to the ground (positive on this tractor) side of the battery, the light did lite up. So on that light it is simply a bad ground. I have ran into this before on 6 volt lights, and I will need to figure out a better ground.

I have bent up the fuse holder bad enough getting it out (only 60 plus years old) that it may not be working now. I am waiting on getting a new one. Now it is possible that a 20 amp fuse will work. Or there is some wire crossed at the switch or near the switch. I would not think any from the switch to the battery or else the crawler would not start. Thanks for the help, and I will keep you posted.
 
This evening I took the wire from the combination switch to the front lights and disconnected it at both end. I put a small 9 volt battery at one end and a ground and then tested the other end with my meter. I am getting electricty through the wire. And I did not see any bare spots on the wire where it might be grounding. Tomorrow I will check and see if there is electricity coming into the switch, although there had to be since the tractor would start. Maybe the switch is wired wrong or there is an internal short in the switch. I do not want to throw money at parts until I figure out what is wrong. Thanks folks.
 
Okay, This morning I worked so I could get to the back of the combination switch. I ran a direct wire from the negative post of the battery to the battery terminal of the switch. Turned on the lights, and I have lights. So, it must be something between the battery and the switch. Someone mentioned that I might have had too light of fuse in the holder, but it is twenty amphs. Now the base of the fuse holder is wired to the voltage regulator and the side to the switch, but I would not think that would matter, as to which end of the fuse the electricity goes out of....but let me know if it does. I am going to replace the fuse holder anyway since I bent it up getting it out of the holder and broke the plastic piece holding it on. Next step is to trace the wiring from the switch back to the battery. Not sure why if something is bad there, the crawler would run on ignition but blow a fuse when the lights turn on. Ummm
 

Got the new fuse and key ignition installed today. Easier than I thought. Front lights work on L, B, and D with crawler not running. Rear light does not work. Crawler started up and the front lights work on L and B and the crawler dies on D. I ran a test light from the negative of the battery to the screw on the back of the rear light (it is a sealed beam). I got a light on the test light so I assume a ground but the rear light did not light up. I assume something internally wrong. Ran out of time. I will trouble shoot in more tomorrow. Troubles me that the crawler dies on D. Do not know why.
 

Got the new fuse and key ignition installed today. Easier than I thought. Front lights work on L, B, and D with crawler not running. Rear light does not work. Crawler started up and the front lights work on L and B and the crawler dies on D. I ran a test light from the negative of the battery to the screw on the back of the rear light (it is a sealed beam). I got a light on the test light so I assume a ground but the rear light did not light up. I assume something internally wrong. Ran out of time. I will trouble shoot in more tomorrow. Troubles me that the crawler dies on D. Do not know why.
 

Got the new fuse and key ignition installed today. Easier than I thought. Front lights work on L, B, and D with crawler not running. Rear light does not work. Crawler started up and the front lights work on L and B and the crawler dies on D. I ran a test light from the negative of the battery to the screw on the back of the rear light (it is a sealed beam). I got a light on the test light so I assume a ground but the rear light did not light up. I assume something internally wrong. Ran out of time. I will trouble shoot in more tomorrow. Troubles me that the crawler dies on D. Do not know why.
 
(quoted from post at 02:57:13 05/29/20)
Got the new fuse and key ignition installed today. Easier than I thought. Front lights work on L, B, and D with crawler not running. Rear light does not work. Crawler started up and the front lights work on L and B and the crawler dies on D. I ran a test light from the negative of the battery to the screw on the back of the rear light (it is a sealed beam). I got a light on the test light so I assume a ground but the rear light did not light up. I assume something internally wrong. Ran out of time. I will trouble shoot in more tomorrow. Troubles me that the crawler dies on D. Do not know why.

I did get the lights to all work. I might have a faulty switch. I ended up connecting the tail light on the same terminal as the headlights on the combination switch. I get brights and dims with all the lights on. The crawler does not die when I switch to dims. What I do not get is headlights without a tail light. I can live with that. I do not have a red light in the sealed beam tail light. If for some odd reason I ever want headlights without a tail light, it is a 2 second job to loosen the screw on the back of the tail light. I still do not know what all was the problem but now things are working. Thanks for all the advice.
 

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