Running lights fuse shorts out

[Garcosta]

Could water getting into the tow vehicle receiver plug cause the running lights on the Motorhome fuse to blow? If not, what is the best way to test with a voltage and ohms meter?

 

[Henry J Fate]

Could water getting into the tow vehicle receiver plug cause the running lights on the Motorhome fuse to blow? If not, what is the best way to test with a voltage and ohms meter?

Inspect all the fixtures to see if any of them are taking in water. Look closely especially the marker lights.

If the coach is over 20 years old, probably will turn out to be a bad fixture.

All the running lights and wiring on the towed vehicle become a suspect if it only happens when towing.

The electrical receiver could be a problem. Grease the pins and receptors with hydraulic grease. The condition of the plug and connector should be considered.

When you are hooked to the tow vehicle, turn the running lights on and go to the connector and move it around to see if you can replicate the failure. With the lights on at night is a good time to visually look at the fixtures for any signs of low light or obscured light.

If the blown fuse is blackened some, that indicates a short.

Make sure all the running lights (towed and mh) combined are less than the circuit fuse.

A multimeter will not help a whole lot for an occasional blown fuse unless it is sustained but even then, you will need to eliminate each/group of possibilities one by one.

 

[Ray-IN]

Disassemble the plug on the rear of the MH and make sure there is not a stray wire not under the screw hold-down. All it takes is one loose strand touching ground.

 

[Garcosta]

Thanks for all your relies! Since I posted that question, I pulled out the receiver plug on my tow vehicle. I found that the installer of my tow system left the wires entering a 0.5” diameter hole in the back of the plug unprotected and open to the elements. When I turned it upside down, water poured out of it. I have taped it up with electrical tape. I will also get some hydraulic grease as suggested to put on the plugs. I still need to inspect the connector wires to confirm if they are corroded but they are only about 18 mos old.

 

[Garcosta]

Omg. Typo. Relies should be replies in first sentence.

 

[Garcosta]

Still need to check if there is a loose wire not screwed down correctly.

 

[DonTom]

Could water getting into the tow vehicle receiver plug cause the running lights on the Motorhome fuse to blow?

I would say NO. The resistance of water is quite high to 12 volts (very low current draw, a fraction of an amp) and the fuse for the running lights will be able to handle several amps.

-Don- Auburn, CA

 

[Larry N.]

Omg. Typo. Relies should be replies in first sentence.

Be aware that you can edit your post and make corrections, so it's not necessary to create another post.

 

[Kirk]

While water does have a high resistance to current flow, that is only true for pure water and since what you deal with is dirty water it is an excellent conductor.

I will also get some hydraulic grease as suggested to put on the plugs. I still need to inspect the connector wires to confirm if they are corroded but they are only about 18 mos old.

As an electrician, I would not use grease in the plug for several reasons, one of them being that it will only be a temporary solution. I am sure that the plug came with some sort of weather plug that the installer failed to use. I suggest that you seal it with a good silicone caulk, and do not completely fill the plug but only seal the opening, extending inside about 1/4" and the outside by roughly the same amount. That will do a far better job and last for a very long time.

 

[NSRV]

I've run into similar issues on cars and trucks, most common cause was incorrect turn signal or brake light bulbs. Try removing certain bulbs and see if the fuse stops blowing. (If it stops, you need different bulbs to fix the issue) If all the bulbs are fine and correct type, then I'd start looking at wiring.

I've also seen a double filament type bulb (commonly turn signal and brake light bulbs) where one of the two filaments blew and fused to the other filament causing a short.

Tow connectors are supposed to be resilient to water, but I suppose its not un-heard of.

If all else fails you could possibly have a wiring issue. If you suspect the tow wiring, I'd start checking there, visually inspect the wiring for snags, frays, loose wires, or melted spots.

 

[Garcosta]

Thanks for all your replies. However, I recently discovered that I don’t think my towing equipment has anything to do with my 20 amp fuse blowing. After getting home towing my car and after unhooking, I went for a drive in the Motorhome 2 times. Each time the fuse for the tail lights, running lights, dashboard lights and fog light blew when I accelerated onto a freeway. Both times the fuse did not blow for the 4 mile local road drive until I got on the freeway. I’m thinking there may be a loose wire that could be shorting against the frame? Could the alternator put out too much power when accelerating onto the freeway? Or could other parts failing? Could it be from my battery rewiring I did over a year ago to wire in a battery shutoff but yet everything was fine for over a year?

I haven’t taken out some of the bulbs but will try that. I can turn off the switch to the fog lights to see if that makes a difference. Then I need to take a look under the Motorhome to look for any wires that may be worn.

Thanks again for everyone’s ideas and suggestions.

 

[Old_Crow]

Start your looking at the truck side of the trailer harness. I've seen lots of butcher jobs when it comes to people installing trailer harnesses in their trucks.

 

[Kirk]

Could the alternator put out too much power when accelerating onto the freeway?

No. The problem is not the alternator.

Could it be from my battery rewiring I did over a year ago to wire in a battery shutoff but yet everything was fine for over a year?

That would be what I would check first. Remember that everything has been working for that year and most of it for longer than that. It is possible that the problem is a frayed wire. Turning off the fog lights to see if that stops the fuse problem is a good first step. It would seem likely that the problem is triggered by vibrations from travel but you won't be likely to find it with a volt/ohm meter when it is intermittent like that. You have not said what chassis you have, as that might help figure things out.

 

[Garcosta]

Start your looking at the truck side of the trailer harness. I've seen lots of butcher jobs when it comes to people installing trailer harnesses in their trucks.

I think I need to provide clarification here. I discovered the Motorhome fails without the trailer hitch harness connected. The receiving electrical connector is factory installed. It looks pretty solid and not loose. I have wiggled the wiring going into that connector and it doesn’t fail.

 

[Garcosta]

No. The problem is not the alternator.

That would be what I would check first. Remember that everything has been working for that year and most of it for longer than that. It is possible that the problem is a frayed wire. Turning off the fog lights to see if that stops the fuse problem is a good first step. It would seem likely that the problem is triggered by vibrations from travel but you won't be likely to find it with a volt/ohm meter when it is intermittent like that. You have not said what chassis you have, as that might help figure things out.

The specifications for my Forest River 32DS FR3 calls out a Ford F53 Gas Class A Motor Home Chassis with a 7.3L 445 cu in V-8. One other thing I had noticed a while ago is that my dashboard lighting seems not bright enough to see the speedometer even with the brightest control set. I wonder if that’s where the problem is. Could the lights in the dashboard be the culprit. I’ll have to figure out where that wiring connector is so I can disconnect it to see if that stops the short issue.

 

[Kirk]

Is the fuse that is blowing the #1 fuse in the passenger compartment fuse panel? You don't say what year model your chassis is but this link will take you to a complete listing of the chassis fuse panels for a 2013 F53 chassis.

 

[Garcosta]

Is the fuse that is blowing the #1 fuse in the passenger compartment fuse panel? You don't say what year model your chassis is but this link will take you to a complete listing of the chassis fuse panels for a 2013 F53 chassis.

Omg I forgot to say the year. Sorry about that. It’s a 2018. The fuse is located in the panel in the engine compartment under the hood or behind the grill and above the engine. It is fuse #6 in the attached photo. I don’t understand why it also takes out the fog lamps and they are not listed in #6 fuse position.

 

[Mark_K5LXP]

It would be my guess that the fog lights were not part of the chassis build, installed by the body fabricator. It would also offer a potential point of failure, something added that may not have been properly installed.

Mark B.
Albuquerque, NM

 

[Garcosta]

I just took the RV for a drive with the fog lights turned off. Went on the freeway as before. The fuse did not blow. So now I need to find the point of connection of the fog lights. That could be the problem.

In addition, when I turn on the light switch, the first position are the parking lights. At this position, the only illumination on my dashboard is the trip odometer and the odometer and in the parking light position those are nice and bright. However, when I turn the switch to lights, those 2 indicators go really dim as are the rest of the dashboard lights. It feels like something is not right about that. That has been like that though ever since I bought the coach. A good question for Ford. Should they operate like that? Thanks.

 

[Kirk]

Should they operate like that?

No. Many of the dashes used in RVs have a large printed circuit board that everything connects through. Most of them have only 1 connection to ground and I am suspecting that is what you have and the problem.