Trailer brake lights not working but turn signals do. 2005 Yukon

[rcecarbldr]

Just recently I lost the brake lights on any trailer I hook up to my Yukon yet the turn signals work, running lights and hazards. It has a 4 pin connector. Yet the trailer brake lights use to work. Any ideas?

 

[Big Mama]

Most likely corrosion in one of the pins or receptacle if they both went out at the same time. Do the brake lights on your truck work? Do your reverse lights work?

 

[rcecarbldr]

Most likely corrosion in one of the pins or receptacle if they both went out at the same time. Do the brake lights on your truck work? Do your reverse lights work?

Everything on my Yukon works. And only the brake lights on the trailer don't work. All else does. Tested two different trailers, same results. I was told this could possibly have something to do with it? I replaced the OEM on last September with one from Amazon but all trailer lights worked till just recently.

 

[Fless]

FWIW the trailer lights go through the turn signal flasher, if that's any help. You can find electrical diagrams on www.charm.li.

Is the 4 pin connector a factory connection? Many of these came with the factory 7 blade trailer connector - yours didn't?

 

[Big Mama]

As @Fless stated if you’re using an adapter the trouble may be there. Your test light can verify. You also may just have a frayed wire there.

 

[GMCChevy]

Start by checking if the brake light pin works at the connector. If your 4 pin was added and you're not using an adapter to go from 7 to 4 start there.

 

[Fless]

Remember that the trailer light circuits are fused separately from the truck body light circuits, but they share some functions with/through the flasher. I'm not saying it's a fuse issue because the turn signals work, and those are the roughly the same as the brake lights.

Are the body turn signal light bulbs different from the brake light bulbs? They are on my '04, but I'm not sure on your '05.

On my body the turn signals and emergency flashers are amber, but the flasher needs to combine the trailer brake light function since the trailer uses the same bulb filament for both turn signals / emergency flashers and the brake lights. It's a trailer light converter of sorts for TV systems that have separate turn signals and brake lights. The flasher works like this 3-to-2 converter:

Tail light converter

 

[rcecarbldr]

FWIW the trailer lights go through the turn signal flasher, if that's any help. You can find electrical diagrams on www.charm.li.

Is the 4 pin connector a factory connection? Many of these came with the factory 7 blade trailer connector - yours didn't?

I bought this used 2 years ago with a hitch and 4 pin connector already on it but everything worked fine up till recently. And the '05's have the same tail lights as the earlier models. The two pins that send power to the Left and Right trailer lights supply power for both which is why this is confusing but I haven't tested for voltage at the pins yet while not connected to a trailer so I'll be doing that later today.

 

[Fless]

The 3-to-2 circuit conversion is done either by the SUV's flasher, or by an aftermarket converter was installed to get the 4-pin plug in place. You have one or the other.

Get underneath and trace the 4-pin harness to see if it simply connects to a body harness, or if there's a converter installed.