Need guidance on why my fuel gauge got scorched

[smilinjak]

the only way the gauge will burn out is if there is a short on the fuel sender wire, or the fuel sender itself shorted out to ground!. there has to be a few ohms to ground to limit the current to the fuel gauge.. also, it's a poor design if the fuse going to the fuel gauge is way too big and allows enough current to burn out the fuel gauge!..

In my 25 years experience of diagnosing electrical problems any time I figured there was only one a problem could happen
I learned there was more than one way��

 

[RickB]

You may be on to something there Rick. Thanks for the assistance..

In my 25 years experience of diagnosing electrical problems any time I figured there was only one a problem could happen
I learned there was more than one way��

Not the first time I’ve seen this. Of course it is a possibility, not a certainty.

 

[MA1920]

View attachment 622343

Don't know if this wiring diagram is different but it is from the I&T FO-46 manual.

My diagram came from the Ford service manual. The diagrams are the same but the components in your diagram are numbered differently. I enclosed the diagram from the Ford manual if you want to see the difference. Oh, Ford didn't label the neutral start safety switch which is number 12 on your diagram.

 

[MA1920]

I had a little time to look at the tractor today. This is what I came up:

When checking resistance across the sender terminals it's 15.1 ohms. Would that eliminate the sender itself as a cause for the gauge to fry?
A complete visual from front to rear showed no visible damage EXCEPT the ignition switch showed a little evidence of critter chewing and one wire had the insulation nicked. I have a photo below. I think a bit of electrical tape will take care of the nick.
When checking grounds, I put one probe on the sender ground and the other to the corresponding pin on the wiring harness. I studied the diagram to get the correct pin. I had continuity. Here is where I think it gets strange, why do I get continuity on multiple pins? Is that normal or is that a clue to guide us somewhere?

 

[radios1]

I had a little time to look at the tractor today. This is what I came up:

When checking resistance across the sender terminals it's 15.1 ohms. Would that eliminate the sender itself as a cause for the gauge to fry? it should, except if the sender is faulty, and grounds out at one spot.
A complete visual from front to rear showed no visible damage EXCEPT the ignition switch showed a little evidence of critter chewing and one wire had the insulation nicked. I have a photo below. I think a bit of electrical tape will take care of the nick.
When checking grounds, I put one probe on the sender ground and the other to the corresponding pin on the wiring harness. I studied the diagram to get the correct pin. I had continuity. Here is where I think it gets strange, why do I get continuity on multiple pins? Is that normal or is that a clue to guide us somewhere?

that just means that other connections are also using a ground..

 

[MA1920]

Over the past few days when I had some free time I continued to keep checking things out. All the wiring is undisturbed with no evidence of critter chewing. In the wiring diagram below, I traced the ground from the fuel sender in green. By studying the wiring diagram, I can see one main ground. It's in the photo below. I checked continuity from the main ground back to the corresponding pin and it was fine. That leads me to believe that the sender may be the source of the gauge frying. I don't want to be just a parts changer, I want to actually diagnose the problem. All comments appreciated.

 

[Scrambler82]

I didn't read all of the postings but I need to ask,"Why do mice eat the wire sheathing" ?
Do they sense the electricity ?
Or is the sheathing the RIGHT material ?

I can't understand why they eat it and for the life of me don't understand why they are even drawn to it.

 

[MA1920]

I didn't read all of the postings but I need to ask,"Why do mice eat the wire sheathing" ?
Do they sense the electricity ?
Or is the sheathing the RIGHT material ?

I can't understand why they eat it and for the life of me don't understand why they are even drawn to it.

I would like to know too. I never had a problem with mice until about 7 years ago.

 

[smilinjak]

Over the past few days when I had some free time I continued to keep checking things out. All the wiring is undisturbed with no evidence of critter chewing. In the wiring diagram below, I traced the ground from the fuel sender in green. By studying the wiring diagram, I can see one main ground. It's in the photo below. I checked continuity from the main ground back to the corresponding pin and it was fine. That leads me to believe that the sender may be the source of the gauge frying. I don't want to be just a parts changer, I want to actually diagnose the problem. All comments appreciated.

The ground wire in the picture looks like it has been undisturbed for a long time. Disconnect it from the engine, shine the ring terminal and the metal it contacts, apply a light film of vaseline or dielectric compound and tighten it down. Carefully check the resistance between the battery negative post and the engine. It should ne zero, clean it the same as stated above.
I should have as this at the outset; had the gauge worked before it smoked. What if anything had been done to the tractor just before it smoked. I have doubt that the sender was the cause but it is possible. There may be a gauge voltage regulator just for gauges that is faulty. You did mention that one of your other gauges was inoperative but not burned I believe. I don’t recall seeing a regulator in your wiring diagram but it would be a good idea to carefully check for one. We will solve this mystery, hang in there.
Smilinjak

 

[smilinjak]

I didn't read all of the postings but I need to ask,"Why do mice eat the wire sheathing" ?
Do they sense the electricity ?
Or is the sheathing the RIGHT material ?

I can't understand why they eat it and for the life of me don't understand why they are even drawn to it.

Wire insulation on modern tractors is made from a plastic derived from soybean oil. Mice like soybeans so they eat insulation for the soy flavor.
Smilinjak