Motor home brake lights work but trailer brake lights don't

[Gerdean]

I have a 2005 holiday rambler admiral se motor home. The MH lights all work. When my husband hooks up his car trailer or any trailer, the turn signals work but the brakes lights do not work. He has talked to rv dealers and shops but no one can figure it out. He was told there is a black box that is a converter and it is only for the brake lights. He cannot find it on the motor home. Can anyone help us?

[Mr_D]

You may have to buy the "black box" (converter) and install it. RoadMaster sells them as do most RV shops.

[Gerdean]

The trailer lights did work at one time on different trailers. Now both trailer's brake lights do not work with the mh. They work with another vehicle.

[sswilson]

There is probably a separate fuse for the lights on the trailer. Mine is a ford chassis and I checked the power at each wire it the trailer connection at rear of MH. I was not getting power one of the wires with signal or brake. Checked under the dash and found I had a blown 10 amp fuse. Replaced and all works well. The trailer lights are not powered with the same lights on MH.

[Easyrider]

2 things to check, first the ground on both the motorhome and trailer and also the ground connection between them. Second is that the black box that's been mentioned is probably available at Walmart and is made to connect a motorhome with amber rear turn signals to a trailer without amber turn signals ( a five wire system to a four wire system) and costs about $20. Good luck with your lights!

[Gerdean]

Ground has been checked. Black box not found. Converter boxes not working.

[FIRE UP]

Gerdean,
This kind of stuff is fun for me. Lets start at the beginning. First, just so we're all on the same page here.
1. Do you have Amber turn signals on the coach?
2. Or, are all your tail light lenses Red?

If you have only RED lenses, the coach will not need a "black box" of any type prior to the trailer plug. The reason, a vehicle with only Red lenses, has what's called combination turn/brake signals. That is, basically, you'll have ONE BULB. And, that bulb will have TWO filaments in it. One filament will be for running lights that will be on all the time the switch for "lights" is turned on.

The second filament, a stronger heavier duty one, will have what's called "dual duty". It will display a turn signal in one situation and, a brake light in another. But, depending on what position your turn lever is in on the column, it can do either one but not both at the same time.

So, now that you have some basics down. Let's look at the trailer plug. That plug, is wired in such a manor that it will mimic what the tail lights on the motor home are doing. So, if you were to sit down at that plug with a 12V test light, you'll see in a just a few minutes, what's working and what's not.

A couple of those little worthless walkie talkies work ok for this test. You have a significant other turn on the ignition. Then, make sure your 12V test light has a good ground. Now, hold that little door open on the trailer plug and have the driver turn on the lights. You probe each pin and find out which one lights up the test light. OK, that's done.

Now, have them turn on one turn signal, probe the remaining pins 'till one is "blinking". OK, that's done. Now, turn on the other turn signal, same probing etc. OK, that's done. Now, making sure that no turn signals are on, have them step on the brakes. You should have "TWO" pins light up. It will be the same pins that were "Blinking" for turn signals.

Now, if you DON'T have any brake light pins light up, there's your problem. A brake light fuse, a brake switch that's gone south permanently, who knows at this point? But, If you DO have two pins light up, then the problem is beyond the motor home.


OK, now back to the lenses. If your coach HAS AMBER LENSES on the back, you will have "TWO BULBS". The one behind the amber one is the turn signal and that's its only duty. But, here's where it gets just a tad bit complicated. Since many toads, are domestically lighted, that is, they only have red lenses, then that system cannot use a separate turn signal/brake signal being sent from the motor home.

So, the signal from the turn signal and the brake, must be combined. And, the way it's done is, through a "Black box". Otherwise know as a "Tail light Converter". If it's there, and working correctly, it will combine a turn signal and brake light together and present them correctly at the back of the toad. But, for now just do the tests and see what you have up to that point. Hope this helps some.
Scott

[Gerdean]

We have amber lights

[FIRE UP]

Originally Posted by Gerdean

We have amber lights

Gerdean,
OK, that's good to know because it helps in narrowing down the way we're analyzing your issue. Now, since you do have separate turn signals from your brake lights, then, if the factory did the wiring for your trailer plug, there's most likely a 100% chance they incorporated the "Black box" or, "Tail light Converter" in the wiring.

But, like I stated in my previous post, before we ASSUME the black box, if it's there, is defective, do the tests I presented. It will take you less than a minute for all of them. And that way, you'll narrow it down right off the bat to either, before or after the trailer plug. Let us know what you find out.
Scott

[FIRE UP]

Gerdean,
Here is what you're looking for:

http://http://www.amazon.com/Curt-Ma.../dp/B001EP0GI6

That little black box is about 2.5" x 2" x .5" thick. You see in the "incoming side" there are three wires, a right turn, a left turn, and a brake light. But, on the outgoing side, you only have two wires. A right turn/brake and a left turn/brake. And those two wires would be wired into the back side of the trailer plug on the coach. So, one way to find it maybe to back trace the RT/brake or, LT/brake from the back side of that trailer plug and follow where they lead you. Eventually it will lead you to that little black box. Hope this helps some.
Scott