Saturday, September 30, 2023


Why are RV’s taillights different brightness, and no brake lights?

Dear Dave,
Our issue is when the back lights on our RV go on, the left one is brighter than the right. But the bigger issue is that the brake lights don’t go on at all. Thank you in advance. — Kathy, Fleetwood Expedition 38K

Dear Kathy,
It looks like your taillight assembly is for both the taillights and the brake lights, which means they would use a dual filament bulb like an 1157.

The first thing I would do is swap the bulbs from the left to right and see what happens. If the left stays brightest, then it is the socket or wiring. If the right is now brighter, then it is the bulb and typically both filaments are lighting up. The 1157 has two pins on the side, one low and the other high on the metal base. These slide down a grove and are twisted and are very difficult to get in backwards. However, I have seen a few cases where the grooves wore out or someone forced the bulb, so make sure they are in the correct grooves.

Most manufacturers have gone to a plug-in style bulb. However, since you did not provide a model year, I can’t track that down. You should be able to pull out the bulb and get a model number. If the socket is bad or loose, you might be able to add a little dielectric grease, which you can get at most auto parts stores in a small packet. Insert a little of that on the base and it helps make a better contact. This is an example of an 1156, which only have one filament, but this gives you an idea what it looks like.

Brake lights not working

To troubleshoot the brake lights not working, first inspect the bulb to see if the filaments are broken. I doubt both sides are bad; however, I’ve learned never to say never when it comes to RVs. If the bulbs look good, use a simple 12-volt light tester and have someone turn on the key and push the brake pedal. This should send 12 volts back to the wires and socket. Make sure you check inside the socket, as that will verify the wire and socket if you have 12 volts, which would mean the bulbs are bad or not getting contact.

If you do not have 12-volt power, then check the automotive fuse, which should be with the chassis fuses. I’m not exactly sure where Fleetwood or REV or whoever they are/were put them. However, most of the time I have found them in a front driver side outside compartment. If the fuse is blown, insert a new fuse and try the brakes. If it blows right away, you have a short in the system somewhere and will need to trace the wiring back to the light assembly. It’s not an easy task and I would start at the back cap, as wires are typically exposed back in that area.

There are many “Gremlins” when it comes to lights such as the wiring, fuses, socket assembly and what else is connected in the automotive loom or casing. I notice you have a large bike rack that could be pinching something, and I would also assume you have a wiring harness for towing a car. This would have wires for the brake lights as a plug in and could have caused a short that blew out the fuse.

Troubleshooting steps. Check:

  • Power at the fuse block
  • Good fuse
  • Power or no power at the light assembly

 You might also enjoy this from Dave 

Why do my RV’s lights only work for a few minutes when unplugged or with generator off?

Dear Dave, 
When my RV isn’t plugged into shoreline power, the lights only work when I’m running the engine or generator. If those are off, the house lights only last a few minutes. Why? Thank you. —Daphne, 2000 Thor Infinity

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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1 month ago

I have issues with tail and brake lights. Mice love to nest in the box enclosure which the lights assy’s. are mounted to; and they love the soy based insulation on the wiring!

I also had a problem with a wire harness under the dash and adjacent to the steering column – this one was tough to find! It turns out the plastic holder which has several wires connecting to it – there was a heater/AC duct pressing down on one corner which happened to be the brake lite circuit wire! Re-arranged it and no more problems.

This is one of those “gremlins” and never say never items! Thanks Dave.

Neal Davis
1 month ago

Thank you, Dave!

1 month ago

C’mon Dave! That pic gives almost zero in do on difference between an 1156 and a 3156. Show us a pic comparing the base ends and your article will have much more purpose. (Also, while on the pic subject, please use an updated pic of sulfated or bulging batteries .. those green messes are getting old and the pic defines nothing useful).
Also, I agree with Tommy … grounds are the biggest culprit in the type of situation posed.

1 month ago

No mention checking for ground that usually is the biggest problem, but you did mention to check the wiring!

Bob P
1 month ago

Your 1157’s are different than mine. Mine have the contacts in the base of the bulb not the side. Plus my brake lights work anytime I step on the brake pedal without turning on the ignition. Since one side is brighter than the other I would guess someone has inserted the bulb backward, I know it’s very hard to do so but I have seen this. Since they didn’t say whether the tail lights were on or off we don’t really know, if the tail lights were off this would be likely the problem.

Joseph Phebus
1 month ago

Stands t o reason, but it should be emphasizes not to drive the RV until the brake light issue is fixed. Otherwise, it’s a rolling bullseye as the driver behind can’t see over the RV and has no chance to apply his or her brakes.

Dave Engstrand
1 month ago

Dielectric grease is an insulator, not a conductor, designed to combat corrosion from moisture. If used, the contacts need to be tight so non remains between them. I recommend Deoxit or similar which is not an insulator.

Bob P
1 month ago
Reply to  Dave Engstrand

Dielectric grease is not an insulator.

1 month ago
Reply to  Bob P

Many articles on the internet and YouTube state that it is not a conductor and too much will inhibit conductivity.

Joe M
1 month ago

I had an issue with no brake lights, after chasing the problem, found out that brake lights won’t work if low air in system. Make sure your coach is aired up, then check brake lights.

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