No right-side brake light on 5th wheel

[dkperez]

I wasn't sure whether this should be a 5th wheel thing or a tech thing, so I put it here...

We have a new Keystone Cougar High Country 246 5th wheel (normal, little 5th wheel).  It has the standard 7 wire plug.  I have NO right-side brake light on the trailer... 

I have TAIL lights on both sides.
I have TURN SIGNALS ON BOTH SIDES.
I have a brake light on the left, but NONE on the right.

I'm not even sure how this is POSSIBLE, since as I understand it, the same wire handles the turn signal and brake light, but I do NOT have a brake light.

I'm making some assumptions:

The trailer, like a car (or my truck) is body ground and just needs hot leads for the lights
If the brake light and turn signal for the right side are the same pin on the plug of the truck, with BOTH should work or NEITHER if there's a problem...  Which clearly is wrong, since the turn signal works and the brake light doesn't

YES, the first thing I did was change the bulb on the trailer...  Just in case.  It's not the bulb
The second thing I did was plug and unplug things repeatedly in case there was poor contact

I checked the plug on the truck, and the pin for the right brake/turn works perfectly (as does the left, the tail lights, and so on).  Push the brake pedal, the pin has power.  Let up, it doesn't.  Turn on the turn signal, it blinks.  So, I presume the problem is SOMEWHERE in the trailer.  The light is a standard 1157 with a brown wire and a green wire.  I presume the trailer is body ground since there are only 2 wires (correct?), and when the lights are on, grounding my test light to the bulb socket works.  As I said, when the turn signal is on, the bright filament blinks, but when the brakes are on I get no right brake light.

I'll call the dealer tomorrow morning and see if they have any brilliant ideas, but it's been my experience that I get a LOT more help and knowledge in here than from the dealer (any dealer)!

So, anybody have an idea what's going on?

 

[RoyM]

First of all, do you have power at the pin on the truck when the right turn signal is on? Use a 12V test light to check. If so, the problem is the trailer. Remove the bulb and see if you have power at the socket, ensure the test light is grounded. If you have power but the light does not work the bulb base is not making good contact with the socket. If still no go, disassemble the plug on the trailer cable and check the connections.

 

[Lou Schneider]

Does your truck have separate turn signals/brake lights or are they combined like on the trailer?  If they're separate you have a combiner to put the stop/tail lights on a single wire.  It could be defective.

Ate you sure you're seeing a turn signal on the right side and not just the tail lamp turning on and off in time with the turn signal? 

 

[dkperez]

Yup, as I said, when I tested the plug at the truck, I ABSOLUTELY had blinking for turn signals, AND solid light for the brake lights on both sides.  I even went BACK out a second time and tested everything on the truck 'cause I couldn't believe the problem was in the trailer...

The truck DOES have separate brake and turn lights, so I'll have to find the place where the "combiner" is.  BUT, at present, it APPEARS that everything on the truck works correctly...

And, of course, the first thing I did was replace the bulb on the trailer.  Then switched the right and left bulbs to verify that there wasn't a bulb problem.

But since the turn signal works on the trailer, doesn't that mean the circuit HAS to be working on the trailer? 

We've had the trailer about a month, and I"m not sure we EVER had good lights.  When we picked it up, the people at the dealer "checked" everything, and turned it over to us already hooked up.  We weren't allowed to back the truck into the shop and hook up.  After that, when we've traveled I've checked the lights, BUT since I'm usually alone doing that, I check them by turning on the 4-way flashers.  I'd always assumed that if THEY worked, I had brake lights.  Coming home from a nearby campground last week, with my wife following me in her car, she called and told me I had a right turn signal but no right brake light.

I'm going to go outside today and do a closer inspection of the assembly on the trailer, and see if I can find anything.  I'll also call the dealer and see if they have any ideas.

 

[Lou Schneider]

If your truck has separate turn signals, you'll have either a 3 to 2 wire converter or a 5 to 4 wire converter mounted on the truck, ahead of the 7 way connector.

These converters combine the brake and turn signals into a single wire to feed the combined brake and turn light on the trailer.  It allows the turn signal to override the brake light on that side, so the bulb continues to flash when the brakes are applied.

The 5 to 4 wire converter does the same thing, but for convenience also sends the tail lights through the box.

A defect in the box that doesn't send the brake signal to both bulbs will cause the problem you're seeing.  The box could work properly feeding a low current test light but break down when supplying full current to the trailer lights.

3 wire to 2 wire converter

5 wire to 4 wire converter

On further thought:

I had something similar happen on my wife's SUV - she added a large carrier with it's own lights to the back, and the shop only wired the combiner on one side.  That combiner was supposed to be used in pairs, one on each side, and I guess they only had one in stock, so the right bulb only had the turn signal and tail light connected to it.

 

[denmarc]

I ran into a problem similar to this a number of years back.  I found that some sockets will accept a 1157 bulb installed 180 degrees off.  The mistake amounted to more than just having the wrong filaments lighting up depending on where the ground for that circuit was.

Just thought maybe this might apply here.  If nothing else, a simple check cost nothing.

 

[Mavarick]

I found that some sockets will accept a 1157 bulb installed 180 degrees off

Yea, and the only way to tell is one light is brighter than it should be. One other thing, remove the bulb and scratch up the socket real good to make sure you have a good ground inside. A test light might show power on the hot tab but a corroded socket will not allow the bulb to work on both filaments. Doesn't make sense but a bad ground does strange things. A small piece of sandpaper always kept the boat trlr lights working. Hope it's something simple.

 

[Water Dog]

I agree with the others that the bulb could be reversed, but in the case that this problem just started without removing or reinstalling the bulb, you might want to try and clipping a test lead to the socket base and a known good ground and see if that solves the problem. If I read your post right, it indicated that it worked when you used your test light in the light socket. That would indicate to me that it is possibly a ground issue.

 

[dkperez]

I can't guarantee it's not something failed in the 5-4 or 3-2 converter, but a: it's been working for 14 years with the old trailer, and b: I have PERFECT brake and tail lights at the PLUG on the truck.............

BUT, I was out there fiddling with the back of the trailer today in the good sunlight.......  On the right side, IN the socket where the two contacts stick up through the plastic holder, on ONE side, the contact WASN'T sticking up.  It was SLIGHTLY recessed into the plastic.  AND, there was a SMALL amount of browning and a little black, sooty powder in the vicinity of the contact.  I SURMISE that the bulb contact isn't making good contact with the socket.  The BRAKE signal is arcing and losing contact VERY quickly, thus the heat (browning) and soot.  The TURN signal, because it only lasts a moment, ALSO arcs but it's going out anyway so it appears to be fine... 

Now, I have absolutely no REAL evidence that this was what was happening, BUT I CUT the wires to the socket and used the test light on the WIRE instead of poking the contact in the socket...  And APPEAR to have power IN the wire........  I"ll get a new socket and try it......

BUT, I ALSO plugged the trailer back into the truck after cutting the wires, so it could ALSO have been some kind of massively weird connection problem between the plugs, but I don't THINK SO.......

In any case, tomorrow I'll get a different socket and give it a try.  AND I"ll spray everything on both sides of the plugs down with electrical contact cleaner.  Just for giggles.

If THAT fails, I'll have to go back to Lou's idea and see if something's going on with the 5-4 or 3-2 converter...

 

[BigDfromTN]

Sounds like you found your issue!

I was thinking it had to be in the socket/fixture as you had power all along the line as required.  As previously mentioned, Grounding issues can cause some strange results.  BUT a bad connector on the "hot" side is essentially the same problem.

Keep us posted.

 

[dkperez]

New socket...  Now have lights............

Of course, since I also had to plug and unplug the truck, it's ALWAYS possible it wasn't the socket, it was something in the plug.  BUT, either way, I DON'T CARE!  They're working and whether it was something truly bizarre as in my poor contact/arcing/losing contact guess, or something more normal, as long as they work I'm happy........

Now my wife wants me to add a SECOND set of tail lights - REALLY BRIGHT ONES up above the originals AND an LED brake light that goes across the middle of the back of the trailer.  She's really big on being VERY visible!

On our old trailer we had two sets of lights, one set up several feet because we carried bikes on the back and you couldn't always see the regular tail lights very well.  On the new trailer we don't carry anything on the back, but she'd STILL like MORE TAIL LIGHTS!!!!!!!!!

 

[lavarock1210]

If you have a GM truck there is a separate fuse for the left and right turn signal to the trailer.  The trailer wiring is on a different circuit and fusing than the truck.