Running lights fuse shorts out

[Garcosta]

So you think it may be the circuit board of the dashboard that may be shorting out? Could the fog lights have anything to do with the shorting out when they are on? I drove it with the fog lights off, and the fuse did not blow out.

 

[Kirk]

So you think it may be the circuit board of the dashboard that may be shorting out?

No I do not. I do not believe that the dash problem has anything to do with the fuse issue.

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.

I believe that the reason for the indications on the dash doing this is due to a defective ground connection and things are find a return though another circuit in place of that ground. Since the fuse doesn't blow if the fog lights are off, they are where that problem is located.

 

[DonTom]

since what you deal with is dirty water it is an excellent conductor.

I wouldn't call several thousand ohms per inch an "excellent conductor" to 12 volts.

FWIW, I have measured the resistance of distilled water (the stuff we can buy), tap water as well as sea water from the Pacific Ocean. The sea water has about half the resistance of the distilled water, tap water somewhat in the middle between the two. But even ocean water is a lousy conductor to low voltages, even with all the garbage in it. No way will you be able to blow even a one amp fuse in series with a dirty water short at 12 volts. You would have to get the water down to twelve ohms to get one amp at 12V. Not going to happen.

-Don- Reno, NV

 

[Kirk]

The sea water has

The conductivity of any liquid is not measured in ohms, as that is resistance and it will depend upon what is dissolved in the water and how much distance is between the probes that you measure with. To calculate the electrical conductivity from the resistance, length and area of the current. The resistivity is given as p = RA/l where p is the resistivity, R is the resistance, A is the area and l is the length. The conductivity is s = 1/p where s is the conductivity.

The following comes from Scientific American.
Is sea water more conductive than tap water?
Explanation: The conductivity of water depends on the concentration of dissolved ions in solution. ... This is because the Sodium Chloride salt dissociates into ions. Hence sea water is about a million times more conductive than fresh water.

 

[DonTom]

The resistivity is given as p = RA/l where p is the resistivity, R is the resistance, A is the area and l is the length. The conductivity is s = 1/p where s is the conductivity.

I made sure the testing was done all the same way, not trying for an exact reading in ohms, mhos or anything else. For comparison only. I used to live near the ocean, so such a test was easy--but not 100% scientific, of course.

But what makes a fuse blow is the current. And plan old basic ohm's law will still apply there. If you have an amp, you have an amp, regardless of what formula is used.

They have to define "fresh water" in the above link. Can we ever find water that is so fresh that it is a million times less conductive than sea water? I kinda doubt it.

If we can take everything out of water, so there is nothing left except H2O, it will not conduct at all. It's the garbage in the water that conducts.

However, I doubt if either of us will ever see water that pure. Not even the million times less conductive.

-Don- Reno, NV

 

[JudyJB]

I was without running lights or tail lights for nine months in 2020 and 2021. I had it "fixed" by a truck repair shop, RV dealer, and automotive electrical specialist that worked on RVs. Each insisted I just needed a new fuse, but fuses lasted only about an hour. Auto electrical guy did trace wiring from front to back, but ended up with the same conclusion about it just needing a new fuse. (I got really tired of arguing with people who supposedly knew the cause of the problem and could fix it.) Finally, I took it to Decatur in late June, and REV factory service took 3 hours to track a crimp in the wiring down and replace it.

Luckily all this time I had headlights, brake lights, turn signals, and backup lights, but I could not drive after dark without running lights or tail lights. Very frustrating.

 

[Garcosta]

Thank you sharing that Judy. Too bad those other facilities couldn’t find it or even more frustrating, they don’t listen to the customer. Your persistence paid off. Glad you were able to resolve it. Your issue with the crimped wiring sounds like it could be similar to mine. I think I tracked it down to my fog lights but now I’m trying to track down where the connector is. I see there are some crimped type connectors in my house battery compartment. I think I’m getting closer to solving it. Thank you again!

 

[Kirk]

I think I tracked it down to my fog lights but now I’m trying to track down where the connector is.

Since the problem goes away with the fog lights turned off, you shouldn't have too much harness to work through. I would try to follow the power from the fog light switch to the lights themselves. It doesn't hurt to look first at the connections and particularly at ones that plug in but don't overlook the light fixtures themselves as something is probably shorting to ground. The light bulb elements are a relatively high resistance to the 12V supply and that resistance is what limits the amount of current flow (amperes) but if a wire or connecter should contact the frame or something connected to the frame, that would become a return path and the current would be very high, blowing the fuse. If you don't find anything at the fixtures or connection points, next examine anywhere the wire passes through the firewall, or anything that could possibly rub against it. Being only 3 years old I would not expect that there has been any degradation of the wire insulation, as happens with very old vehicles. It could be some poor workmanship that took 3 years to show up.

If you wanted to do another test just to verify that your problem is in the fog lights you could take it for a drive in the daytime with only the fog lights on, but I think you are right in your thinking at this point.

 

[Garcosta]

Good points. I’ll give it another drive with only the fog lights on. I had not tried keeping the running lights off but fog lights on. Good idea. Thanks.

 

[JudyJB]

One possibility if all else fails--most truck and auto manufacturers use only a handful of different wiring harnesses. In other words, they don't make a specific wiring harness for each vehicle. So, depending on how many electrical gadgets your vehicle has, there are likely to be extra wires in that wiring harness that are not used for anything.

You might be able to get someone to find one of those unused wires and rewire your running lights. That was going to be my suggestion if the factory folks could not find a cause, but I suspected it would be more complicated and take a lot more time.

And by the way, I thought it was strange that my tail lights and running lights ran on the same wire. Wonder what the connection might be with your fog lights and running lights??? Very strange that running lights work only when fog lights are off, at least I think that is what you are saying.

I also had wondered if the running lights were wired such that a bad connection in one could cause them to all short out, but that was not the case, at least in my situation. I have had one running light need a new bulb in the past, but this was the first time all went out at the same time.

 

[Garcosta]

To clarify about the tail/running lights and fog lights, the failure occurs when I’m gettin on the freeway. Prior to the freeway all lights are working. But when I get in the freeway and accelerating to freeway speed the fuse blows. However, if I leave the fog lights off, the fuse doesn’t blow when getting up to freeway speed. That’s a good idea to see if there are some vacant wires to use. I’ll be checking the bulbs and connectors of the fog lights and find the connection.

 

[DonTom]

To clarify about the tail/running lights and fog lights, the failure occurs when I’m gettin on the freeway.

What type of fuse is it that is blowing, current rating, fast blow, slow blow etc. ?

Are you sure it is the exact type of fuse it should be in every way? There is more to fuses than the current rating.

Also, the numbers of all the lamps involved (and how many) would help.

Could it be the normal load of the lamps is above your fuse rating?

-Don- Reno, NV

 

[Garcosta]

The fuse is 20 amp mini 2 prong fuse. The only one that fits and according to the specs. Im pretty sure it’s the right fuse. However, I think I have isolated the problem. First off, I can’t drive the rv with just the fog lights on. They are wired to the lights that turn off at the switch. I can only drive without the fog lights while the running lights are on or with the fog lights and while the running lights are on. In the compartment where my house batteries are located there are a huge bunch of wires in what resembles as corrugated plastic that the wires are in with many zip tied together. There are 4 wires not in the plastic sheathing that I wiggled around but no luck getting the fuse to blow with all lights on. I rearranged a bit of about ten sheathings with wires in them that are zipped tied to the frame with non-sharp edges. Plus, I could not see any bare wires in that area touching the frame.

After I zip tied some of the wires together and moved/shifted the big group of wires in sheathing a bit, I took it for another test drive with no failures. I still have not isolated the exact problem so I could get it to fail but right now it’s all working fine.

Thanks for so many of all your comments and recommendations. Wish I could tell you I found the issue but I think I’m getting warm.

 

[DonTom]

First off, I can’t drive the rv with just the fog lights on.

Are they stock, as came with the RV?

If you can list each type of bulb that is on while the fuse blows, we can add up the currents and see if the fuse should blow or not.

-Don- Reno, NV

 

[Garcosta]

All the lights came with the rv when I bought it new. Here are the bulbs with the count total for each, identifier and the Watts that I looked up. I added photos as well.

Tail lights- total 4 bulbs, each 26.9W, Tot 107.6W CEC-3157
Fog lights- total 2 bulbs, each 40W, Tot 80W GL-995 (02 19667)
Running lts- total 13 bulbs, ea. 4.9W, Tot 63.7W SAE-AP2-00
Total Watts = 251.3W
So approximately 20.92 Amps ?

It’s a bit above that because I didn’t include the dashboard lights.

 

[uchu]

Change tail and fog lights to LED.

 

[DonTom]

So approximately 20.92 Amps ?

Well, that explains why the 20 amp fuse blows. So one simple fix is to replace the fuse with a 25 amp, if the lamp wire to the fuse is at least 10 AWG or thicker, if you cannot change to LED.

-Don- Reno, NV

 

[Ray-IN]

The fuse is 20 amp mini 2 prong fuse. The only one that fits and according to the specs. Im pretty sure it’s the right fuse. However, I think I have isolated the problem. First off, I can’t drive the rv with just the fog lights on. They are wired to the lights that turn off at the switch. I can only drive without the fog lights while the running lights are on or with the fog lights and while the running lights are on. In the compartment where my house batteries are located there are a huge bunch of wires in what resembles as corrugated plastic that the wires are in with many zip tied together. There are 4 wires not in the plastic sheathing that I wiggled around but no luck getting the fuse to blow with all lights on. I rearranged a bit of about ten sheathings with wires in them that are zipped tied to the frame with non-sharp edges. Plus, I could not see any bare wires in that area touching the frame.

After I zip tied some of the wires together and moved/shifted the big group of wires in sheathing a bit, I took it for another test drive with no failures. I still have not isolated the exact problem so I could get it to fail but right now it’s all working fine.

Thanks for so many of all your comments and recommendations. Wish I could tell you I found the issue but I think I’m getting warm.

Your explanation points directly to a chaffed wire - somewhere in those bundled wires.