15 Amp 12 V fuse randomly blows w no activity (or not)

**stroguy** · 01-18-2023, 03:08 PM

Originally Posted by llr2800

Not a bad idea but the fuse will probably blow quicker then the meter reacts.

I suggest connecting a 12v incandescent light (old school taillight) in place of the fuse. Then bang shake move everything you can. The light may be on an dim until you trigger the short, then it will be bright. The more you can trigger the bright bulb the closer to the issue.

Of course hopefully the wire you found by the furnace is the issue and you are done.

My meter has a hold function to snapshot the highest reading(s). Guess I should have added that function is helpful. If doing the checking solo.

**Bob Chamberlin** · 01-18-2023, 04:12 PM

Thanks for your thoughts. Very much appreciated. All of the appliances in question are powered by either gas or 110 V AC. The 12 V circuit in question only provides enough power for control signals and ignition spark for the refrigerator and furnace (other than a couple of never used LED puck lights so I am doubting that the circuit is overloaded. That said, it appears that the problem is likely resolved although I will remain skeptical. A bare spot on a wire next to a frame member at the furnace has been found, repaired and re-routed. I won't know for sure until a lot of time passes with no more problems in the circuit.

**Mr. Goodwrench** · 01-22-2023, 07:07 PM

Originally Posted by Bob Chamberlin

Thanks for your thoughts. Very much appreciated. All of the appliances in question are powered by either gas or 110 V AC. The 12 V circuit in question only provides enough power for control signals and ignition spark for the refrigerator and furnace (other than a couple of never used LED puck lights so I am doubting that the circuit is overloaded. That said, it appears that the problem is likely resolved although I will remain skeptical. A bare spot on a wire next to a frame member at the furnace has been found, repaired and re-routed. I won't know for sure until a lot of time passes with no more problems in the circuit.

Hopefully your problem is solved. For the rest of us, this thread has provided a wealth of troubleshooting tips.

**ScottK** · 01-25-2023, 03:06 PM

An exposed wire getting wet can cause that. Even just a cut end.

**ExNihilo** · 01-26-2023, 06:08 PM

Just by chance is that a 12v refrigerator? Some were installed with a smaller gauge wire which typically blow the inline fuse to the fridge. If it is a 12 VDC fridge look at the wire gauge.

Apologies, I did not read all threads- I see they are 110v

**Haznavy** · 12-25-2023, 12:12 PM

Bob,

I'm having this exact same issue. What did you end up finding out and what was your fix?

**Second Chance** · 12-25-2023, 01:48 PM

Originally Posted by Haznavy

Bob,

I'm having this exact same issue. What did you end up finding out and what was your fix?

@Bob Chamberlin hasn't logged into the forum since January. Quoting someone (as I have done with you here) or tagging someone (as I have done with Bob Chamberlin) will generate an email notification that they might see.

Rob

**Bob Chamberlin** · 12-26-2023, 01:30 PM

Thanks to the many people who have responded to my initial Post. Since I did not see any responses in the first week or two I stopped looking at this forum. For those who have asked, this is to explain what my resolution has been. My problem was with a single 12 V fuse randomly blowing when there was no motion of any kind in the trailer (or when it was going down the road). IE: No predictably repeatable cause. First, I found a frayed wire brushing the frame of the gas heater. Fixed it with heat shrink tape and re-routing but that turned out to NOT be the real problem cause. In my initial post I said that the items on the affected circuit were, 1) refrigerator (which is 110 V and/or gas) but which has control signals using 12 V, 2) thermostat (meaning that control signals to the gas heater and both AC units were unavailable), 3) CO/Propane alarm. My thinking was that any of these items could have been the problem or it might be a wiring problem. Without a refrigerator or a gas heater the trailer was unusable especially in the winter months. Following my initial post I also found that the right rear brake/turn signal light was out and replacing the LED fixture did not fix the problem. Replaced the thermostat (yes, they do break down anyway after five to ten years). Did not fix the problem. Disconnected the CO alarm. No help there either. Found that there was a significant hydraulic leak near the right side center jack. Note that this had nothing to do with my 12 V problem but I had to fix it. Had to remove the underbelly. Replaced the fluid soaked insulation and found that Grand Design had installed the hydraulic line in direct rubbing contact with the rotating slide gear mechanism. Re-routed the line and replaced it with a 20,000 psi dump truck hydraulic line. This powers both living room and kitchen slides. The reason why this is all relevant to the 12 V fuse problem is that while in the underbelly I found a 12 V electrical line that was routed such that it was repeatedly "pinched" by the Kitchen slide mechanism. Replaced a section of the 12 V line and re-routed it. ALL SYSTEMS NOW WORK PERFECTLY. Note: When I reconnected the CO/Propane alarm it acted very "flakey" so I have replaced it and now all is well. (There is a printed message on the CO alarm that it needs to be replaced every five years anyway.) Summary: I blame Grand Design for two assembly issues. One was the hydraulic line that was rubbing on the slide mechanism and the other was an electrical line that was being pinched by a slide mechanism. Other than that I am otherwise delighted with the design and construction of my 310GK. One last note: The power converter (which converts 110V power to 12V to charge your batteries and power many systems in the trailer died. Fairly new GSM batteries died. (They do not like to go all the way down.) Replaced power converter and installed new batteries. NOTE: Local RV repair person indicated that Power Converter failure is more common than it should be. Knowing this it is hard to understand why it is so difficult to get to the location in which the Power Converter is installed. Replacement took me two days.

**Haznavy** · 12-27-2023, 04:50 PM

Originally Posted by Bob Chamberlin

Thanks to the many people who have responded to my initial Post. Since I did not see any responses in the first week or two I stopped looking at this forum. For those who have asked, this is to explain what my resolution has been. My problem was with a single 12 V fuse randomly blowing when there was no motion of any kind in the trailer (or when it was going down the road). IE: No predictably repeatable cause. First, I found a frayed wire brushing the frame of the gas heater. Fixed it with heat shrink tape and re-routing but that turned out to NOT be the real problem cause. In my initial post I said that the items on the affected circuit were, 1) refrigerator (which is 110 V and/or gas) but which has control signals using 12 V, 2) thermostat (meaning that control signals to the gas heater and both AC units were unavailable), 3) CO/Propane alarm. My thinking was that any of these items could have been the problem or it might be a wiring problem. Without a refrigerator or a gas heater the trailer was unusable especially in the winter months. Following my initial post I also found that the right rear brake/turn signal light was out and replacing the LED fixture did not fix the problem. Replaced the thermostat (yes, they do break down anyway after five to ten years). Did not fix the problem. Disconnected the CO alarm. No help there either. Found that there was a significant hydraulic leak near the right side center jack. Note that this had nothing to do with my 12 V problem but I had to fix it. Had to remove the underbelly. Replaced the fluid soaked insulation and found that Grand Design had installed the hydraulic line in direct rubbing contact with the rotating slide gear mechanism. Re-routed the line and replaced it with a 20,000 psi dump truck hydraulic line. This powers both living room and kitchen slides. The reason why this is all relevant to the 12 V fuse problem is that while in the underbelly I found a 12 V electrical line that was routed such that it was repeatedly "pinched" by the Kitchen slide mechanism. Replaced a section of the 12 V line and re-routed it. ALL SYSTEMS NOW WORK PERFECTLY. Note: When I reconnected the CO/Propane alarm it acted very "flakey" so I have replaced it and now all is well. (There is a printed message on the CO alarm that it needs to be replaced every five years anyway.) Summary: I blame Grand Design for two assembly issues. One was the hydraulic line that was rubbing on the slide mechanism and the other was an electrical line that was being pinched by a slide mechanism. Other than that I am otherwise delighted with the design and construction of my 310GK. One last note: The power converter (which converts 110V power to 12V to charge your batteries and power many systems in the trailer died. Fairly new GSM batteries died. (They do not like to go all the way down.) Replaced power converter and installed new batteries. NOTE: Local RV repair person indicated that Power Converter failure is more common than it should be. Knowing this it is hard to understand why it is so difficult to get to the location in which the Power Converter is installed. Replacement took me two days.

Bob,

Thanks for the detailed description of things to look for. My problem, thankfully, was chalked up to a rather sizable rat who managed to get himself lodged between the heater fan and housing causing the fan to seize and blow the fuse. Removed the rat, fixed the problem. If only all our problems could be fixed so easily.