L3540 Blowing Head Light Fuse

[ShogunKC]

I noticed last week that the head lights weren't working and found the fuse blown. I replaced it and it immediately blew, so I figured there was a short somewhere.

I removed the console covers so I could get access to all the connectors and switches in the dash. I disconnected all the battery ground, lights, switches, and instrument panel and started to check for a short with my multi-meter looking for continuity at each of the connectors. I noticed that I would get a short to ground at the head lights whenever I turned the head light switch on (after connecting the switch). But, when I checked the connector, no shorts in the head light wiring. I briefly put in a 30 amp fuse and the head lamps would work but I noticed that the wiring going into the turn signal switch were getting warm. That gave me a place to start looking next.

I found that a Green/Red wire going into the multi-function combination lever (the head light & turn signal switch) was shorted to ground. I double checked to make sure I didn't have lights connected that would give me a continuity reading, and there were no lights connected. Looking at the wiring diagram, this wire also goes to the Hazard Switch, the instrument panel, and the rear combination lamps. I looked at all the wiring harnesses and wires that I could visibly see and couldn't see any worn wiring or anything that would indicate a short to ground.

On a whim, I disconnected the Green/Red wire from the light/turn signal switch and tried the head lights and found that I no longer blow fuses. But, it seems that I have lost the rear red tail lights and I'm guessing the headlight indicator on the instrument panel (and possibly switches that light up when the lights are turned on).

Just curious if there might be an easy way to figure out where this short might be. I don't ever drive the tractor on the road, so having rear tail lights isn't really that big of a deal, at least for now. This is bugging me more than anything else. Actually, I feel that the work lights provide much better lighting than the head lights anyway because the loader out front tends to block the headlamps.

I read a few threads about shorts and fuses - the one that looked the best had a bunch of talk about resistance readings, so it seems that's where I might have to go next? Just hoping for a few suggestions on how to narrow down the location of the short.

Thanks!

 

[ShogunKC]

Been noodling over my problem this past weekend. I looked at the wiring schematics and am puzzled by what appears to be a connector in the diagram but unsure where it goes - the diagram does not have any description for the connector unlike the instrument panel connectors.

I am guessing that it's a connector to the cab wiring harness that goes into the roof. If that's the case, any idea where this connector is located? If the green/red wire shows a connection to ground and I haven't removed all the lights in the circuit, it'll keep showing a short until I disconnect everything and then test wire-to-ground continuity. (I think that's accurate logic).

 

[Dave_eng]

Your test to ground can be misleading in this respect.

If there is a bulb in the light socket, the bulb filament is providing the connection to ground. It is a high resistance connection because the resistance is what produces the light.

Testing with the bulb removed may be more helpful.

Dave

 

[ShogunKC]

Your test to ground can be misleading in this respect.

If there is a bulb in the light socket, the bulb filament is providing the connection to ground. It is a high resistance connection because the resistance is what produces the light.

Testing with the bulb removed may be more helpful.

Dave

I thought that I disconnected all the switches and bulbs when I was troubleshooting, but wondering if I missed some in the cab roof. The schematic shows a connector that's not labeled - I *think* that it goes to the cab roof but I'm not positive.

 

[Dave_eng]

Can you advise on the type of transmission and if your tractor has a cab.

I suggest the following to you to try and locate the reason for a fuse to keep blowing.

Remove all the light bulbs on the fuse circuit (head lights, tail lights, signal lights) and then activate the switches to see if a fuse blows.

This test should tell you if there is a short to ground in the wiring if a fuse still blows.

Replace the bulbs one at a time while exercising the switches to find which bulb is associated with the fuse blowing.

Hopefully as you replace bulbs and power circuits something will suddenly blow providing a clue.

Dave

 

[ShogunKC]

Was at the dealer yesterday and was able to talk to a tech about the connector on the schematic. He was a little confused as well because their shop manuals are also not labeled as to what the connector is and where it goes.

He was pretty sure that it went to the cab roof but had not idea where the connector was. He did say that there would be one so that you could completely remove the cab during service that required that. He thinks that it's likely low on the cab somewhere around where the wiring harness goes up one the pillars into the roof.

He said that it could also be water that got into wiring under the floor mats, but I couldn't find any wiring under the floor mats.

So, I'm still on the hunt for this wiring harness connector.