Brake lights challenging me!

Hi there, new member here, fresh from the intro thread! My 1992, 22' is having a weird issue with the brake lights/right turn signal.

-With the driving lights off, the brake lights seems to work properly.
-Driving lights on, all the brake lights illuminate to a lower level, like running lights (including the high, center light) and get brighter with brake applied.
-left signal works fine
-right signal flashes, AND all the marker lights (same with hazards)
**although it is as above at present-at one point, the right signal would be bright with driving lights, and go off with brake application.

So it seems that there is a weird connection between the right signal and the driving lights. I read something about a relay in the rear lights circuit or something, but I haven't seen one and don't know what it would do.

Things I've tried:

-checked the bulb
**it looks like the socket for a two contact bulb, but the bulb only has one contact. Same with the left-which works. I tried to switch it out for two contact but still not right
-checked the ground for the fixture and reconnected
-switched wires at fixture for good measure (back to original now)
-Replaced the pigtail to tow vehicle
-used two different vehicles
-checked all grounds at the frame for pigtail/trailer wiring to frame
-disconnected each pigtail connector, one at a time to troubleshoot
-disconnected hot wires from tow vehicle lead/fuse to test.
-blue brake looking wire that seems to go towards the converter (?) was disconnected for test (blue to brakes along propane line still connected-brakes work)
-lead from fuse to (new) break-away unit disconnect for test.

I'm wondering if it really is the bulb some way, and what the original bulb spec is.
Is there a relay that is bad somewhere?
Is it really just a mixed up wiring job?

I'm hoping this is a common and simple problem...

Hi and welcome! I think your trailer wiring is quite possibly screwed up. There are NO relays in the trailer that do anything for the running/turn/brake signal lights. These lights get all their power and function entirely from the tow vehicle. The brake/turn signal lights are normally 1157 lights, with two positive contacts in the base. If you are seeing ones with a single contact, it's most likely an 1156 bulb, which has only one filament.

In the trailer, the blue wire is normally the path from your tow vehicle's brake controller to the trailer's electric brakes. It is NOT connected to the lights in any way.

If you see white wires, they are normally the ground lines. You should see white wires at all light sockets as I recall. Usually, green wires are the positive feeds to the trailer's running lights (tail and side/front marker lights). Those lights would be on anytime you have your tow vehicle parking/headlights on. If your tow vehicle has DRLs and they illuminate the tow vehicle's tail lights, then they may come on with the DRLs too.

The brake/turn light wires are normally colored brown for one side and red for the other.

Unfortunately, HiLo did not ALWAYS stay with this wire color convention, but if you find those color wires at the sockets, you now know what they are. And you should see the SAME color positive wire to each tail light to provide running light power. The different color wires at each socket are brake/turn.

From your post, I'd say the first thing you might try is to replace the brake/turn bulbs with 1157s.

- Jack

Thanks Jack! Now I know about the 1157s, so that'll help! I'm gonna try that first. The whole connection with the drl is confusing in my situation. I can't really get to the wiring inside, so I'm gonna hope they just run straight with no junctions end to end and try to use a multimeter to test

If you buy a simple turn signal flasher (at an automotive store) you can do a quick test of ALL the running light circuits in the trailer. Simply plug it into the trailer plug at the 11 and 1 O'clock position and it will send trailer battery voltage to all those lights. They will flash too, which makes this a great way to warn other motorists if you have a highway breakdown. Here's a link to the way the trailer (and tow vehicle) plugs are supposed to be wired, and it shows the standard wire colors that are supposed to be used too: https://www.google.com/search?q=7+b...iw=1005&bih=478&dpr=3.33#imgrc=atCzF4pwhl7U6M

If you plug it in to the 11 and 9 O'clock blade positions, it should cause the right turn/brake light to flash.

If you make a couple jumper wires for the flasher, so that you can connect the 11 and 3 O'clock blade receptacles together, the left brake light should flash.

Of course you can just use a jumper wire to connect the 11 and 1 positions together and then use it to connect the 11 and 9 and finally the 11 and 3 O'clock positions to test all the circuits, but they won't be flashing without the flasher, which is a nice feature.

There's no danger doing this - you're simply feeding battery voltage to the light bulbs, which is what the tow vehicle does when the trailer is connected to it. You're just using a different battery.

I think I may have given you an incorrect color in my last post for the left turn circuit in the trailer. The HiLo wiring diagram I was looking at shows it as red, but the "standard" color is yellow. You might find either one. I THINK mine is red though.

- Jack

Hey Jack! I got it fixed! And the problem was... Wait for it... The bulbs! I was trying to rationalize the use of the single contact bulbs, since they were in both fixtures and the left one worked. I'd tried the double contact LEDs I bought for the interior, which made other weird problems. I don't know where my manual is and thought the forum the best place to get info about what is the proper bulb-and identify my symptoms. It WAS the 1157 after all! I'd read somewhere else where you'd posted about the signal tester, and am intrigued.
Now I've got my problem solved and we documented some weird things that can happen with the wrong bulbs!
Now I'm going to try to share some pics soon of my trailer. Got another trip coming up in a few days!

Thank you!

I'm so glad it was so simple. Just a note though, you CAN use 1157 replacement LED bulbs in the Bargman receptacles. If you check specs carefully, you can get bulbs that are brighter and will be safer than the way incandescent bulbs work in those housings. I did that after I found and corrected the rat damaged wiring in my trailer.

- Jack

That's good to know. I've replaced all the interior lights with LED, but not the exterior, as they run off the alternator. I suppose that the trickle to the trailer battery might be a little greater with less incandescent draw.

RainyDayDragon said:

That's good to know. I've replaced all the interior lights with LED, but not the exterior, as they run off the alternator. I suppose that the trickle to the trailer battery might be a little greater with less incandescent draw.

Click to expand...

Yes, but that's only a factor if your tow vehicle lights are on or if your DRLs light the trailer lights - then it's a rather big draw. I simply wanted more obvious brake and trailer lights, and the LEDs gave that to me.

As a digression though, last year I replaced the Bargman fixtures with LED ones I got from etrailer.com. They are slightly larger and MUCH more bright. It was a simple mod - although I had to add a separate light fixture for the license plate (also LED).

- Jack