Converter 12V fuse blowing only after towing

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Yoshi

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Hi,

I have a small travel trailer with a WFCO 8735. After a days towing, the same fuse #5; 15 amps is always blown. Once I replace the fuse and hookup to shore power, the fuse will not blow again (til towed). I've used contact cleaner and a small amountof dilelectric grease on both the RV and tow 7 pin connector.

It seems like something is shorting out in the same circuit everytime I tow.

Can someone provide some techniques of how to run this to ground (no pun intended).

Thank you
 

Mark_K5LXP

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What circuit(s) do fuse #5 supply? Does the fuse blow upon connection to the tow vehicle, during braking, when turn signals activated or other specific operation?

Mark B.
Albuquerque, NM
 

SpencerPJ

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My guess you have a ground problem. Check ground from battery to frame, and ground by fuse box.
 

Yoshi

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What circuit(s) do fuse #5 supply? Does the fuse blow upon connection to the tow vehicle, during braking, when turn signals activated or other specific operation?

Mark B.
Albuquerque, NM
Hi, The #5 is for a control panel that turns on lights in the RV (with rocker switches), toilet pump and fan. I have not checked if it's tied into any specific action from the tow vehicle. I will try and do that. It’s good while on shore power, I disconnect, plug in the 7 pin and do my driving for the day. Upon arrival at the camp site it’s blown.
 

Yoshi

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My guess you have a ground problem. Check ground from battery to frame, and ground by fuse box.
Ground on the RV side…correct? Fuse box in tow vehicle or the converter? The 7 pin on my trailer goes to a bus bar (in a box) on the frame of the RV, the RV battery connections go to the bus bar also.
 

Yoshi

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Hi, The #5 is for a control panel that turns on lights in the RV (with rocker switches), toilet pump and fan. I have not checked if it's tied into any specific action from the tow vehicle. I will try and do that. It’s good while on shore power, I disconnect, plug in the 7 pin and do my driving for the day. Upon arrival at the camp site it’s blown.
I’m on an overnight stop now. I disconnected shore power, plug the 7 pin in and turned the signals on, headlights and press the brakes and it did not blow.
 

SpencerPJ

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Ground on the RV side…correct? Fuse box in tow vehicle or the converter? The 7 pin on my trailer goes to a bus bar (in a box) on the frame of the RV, the RV battery connections go to the bus bar also.
Ground on RV side
Fuse Box at converter
Sure sounds that something is loose causing a fuse to pop, stationary it plays nicely. I would continue to look for loose wires and connections. In the mean time, have spare fuses. Good luck.
 

tlmgcamp

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It might be a short that only occurs while bouncing around during travel. A wire frayed by critters?
 

Yoshi

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Ground on RV side
Fuse Box at converter
Sure sounds that something is loose causing a fuse to pop, stationary it plays nicely. I would continue to look for loose wires and connections. In the mean time, have spare fuses. Good luck.

Do you think it has to do with the ground on circuit #5 since it is the always the one that blows and no other. tks
 

Pedro Dog

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I disconnected shore power, plug the 7 pin in and turned the signals on, headlights and press the brakes and it did not blow.

Was the engine running?

I assume the the trailer was not connected to the tow vehicle. That's a separate ground path.
 

CharlesinGA

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Well, as you noted, the fuse has nothing to do with the 7 way or the tow vehicle. Are you sure you are turning off the fan, water pump, lights, etc before towing? Thats a lot of load on one circuit. Does the trailer run properly off of the battery (ie. no shore power, and no tow vehicle connected).

Charles
 

Yoshi

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Was the engine running?

I assume the the trailer was not connected to the tow vehicle. That's a separate ground path.
Yes the engine is running. Thetrailer is connected to the tow vehicle when the fuse blows.
Well, as you noted, the fuse has nothing to do with the 7 way or the tow vehicle. Are you sure you are turning off the fan, water pump, lights, etc before towing? Thats a lot of load on one circuit. Does the trailer run properly off of the battery (ie. no shore power, and no tow vehicle connected).

Charles
Hi, Yes, everything 12V was off. There are no other 12V items running while towing other than the refrigerator (different fuse) and the CO monitor (same fuse that blows).

There is a small red light that indicates when the fuse blows. I was reading that a load is usually on when the red light is lit for the blown fuse. But like, I mentioned, everything for that circuit is off except the CO monitor.
 

tlmgcamp

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Yes the engine is running. Thetrailer is connected to the tow vehicle when the fuse blows.

Hi, Yes, everything 12V was off. There are no other 12V items running while towing other than the refrigerator (different fuse) and the CO monitor (same fuse that blows).

There is a small red light that indicates when the fuse blows. I was reading that a load is usually on when the red light is lit for the blown fuse. But like, I mentioned, everything for that circuit is off except the CO monitor.
Pull the CO detector and disconnect it. I would think it odd for that to fail, but it would take it out of the equation, or find the problem.
 

SpencerPJ

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Pull the CO detector and disconnect it. I would think it odd for that to fail, but it would take it out of the equation, or find the problem.
I agree, and it could be any number of the switches. With 12vdc power live, not plugged into AC, I would start wiggling various wires, trying to simulate road vibrations / bumps, looking for a short.
 

Yoshi

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*Update* When I left this morning with the vehicle running , I plugged in the 7 pin and the fuse blew. Ah ha, I tried it a second time and it did not repeat/blow. I then plugged it in with the vehicle not running and it also did not blow. Drove about 1/4 mile and checked it and it was blown.

So, it first blew just plugged in before driving, then it didn’t a second time, but then blew after driving just a very short distance.

Which ground wires on the converter should I check.

Tks for the help
 

SpencerPJ

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*Update*
Which ground wires on the converter should I check.

Tks for the help
You are doing good detective work. Personally, I would go over every single connection I could find. What other fuses do you have and what do they control. It sure seems like something only on your #5 circuit, the initial plug in to TV is just the extra umph to the system to blow the fuse. It could be a ground, or a positive wire rubbing a ground.
 

Kirk

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Do you think it has to do with the ground on circuit #5 since it is the always the one that blows and no other. tks
The ground isn't the problem. A ground is the return side of the circuit and if it was bad there would be no current flow and things wouldn't work but the fuse would never blow. Since it only happens when towing you clearly have a short somewhere that is probably shorting to ground and thus causing the fuse to blow. It could be anything from abraded insulation to a bare wire but as Gary has suggested, something is moving when you travel. It could also be a problem in the trailer plug or the socket on the tow vehicle. If you know someone who could tow the trailer for you, a good test would be to see if your friend towing the trailer would cause that fuse to blow. Is the #5 fuse in the tow vehicle or the trailer? Do you have a copy of the WFCO manual to use?
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