Help... Trailer Brake Light Will Not Work

Frozen001 · June 20, 2007

OK so I hooked up the trailer last night to make sure everything was OK before the trip. Everything worked except the Right Trailer Brake light. The right signal works and when I use the 4-way flashers work, so it IS NOT THE PLUG, BULB, OR FUSE. ONLY the right BRAKE light does not work. I have no Idea where to even start looking. BTW the truck break lights work fine, and it is a GMC 2004 2500HD Regular Cab.

So far I know this:

Used a test light and I know the following:

1) The right pin on the trailer plug only lights up the test light with the signal

2) The fuse in the truck on the drivers side for the right turn/stop light will light the test light only with the turn signal, while the left will light with the turn signal and break light.

ANY help would be great as I only have till Friday to get this working.

pwall · June 20, 2007

On my trailer, the brake light and signal lights, although the same bulb, it actually a double filament bulb. Thus, your brake light can be out, but not the signal light.

I would try changing the bulb and see what happens.

asilverblazer · June 20, 2007

The brake and signal light use the same filament in the bulb, the tail light uses the other filament (the dimmer one). Somebody else just had this problem, but I don't recall the solution.

pwall · June 20, 2007

ah yes, you're right. how dumb of me.

Frozen001 · June 21, 2007

Well I dropped it off to the dealer last night... Just got a call from them... They said it was the "flasher module"... I have not picked it up yet, but hopefully it works when I do.

asilverblazer · June 21, 2007

Flasher module, haven't even heard of that one. Any more details on it? I wonder if my '99 has one... Sounds like a neat part.

Frozen001 · June 21, 2007

Flasher module, haven't even heard of that one. Any more details on it? I wonder if my '99 has one... Sounds like a neat part.

No details... From what they told me it is behind the fuse panel, and it controlls everything. I am assuming what it does is convert from a 4 light to a two light seeing how my truck has a seperate signal and brake lights and on trailers there is a combined signal/break light.

bevecorp · September 15, 2007

OK so I hooked up the trailer last night to make sure everything was OK before the trip. Everything worked except the Right Trailer Brake light. The right signal works and when I use the 4-way flashers work, so it IS NOT THE PLUG, BULB, OR FUSE. ONLY the right BRAKE light does not work. I have no Idea where to even start looking. BTW the truck break lights work fine, and it is a GMC 2004 2500HD Regular Cab.

So far I know this:

Used a test light and I know the following:

1) The right pin on the trailer plug only lights up the test light with the signal

2) The fuse in the truck on the drivers side for the right turn/stop light will light the test light only with the turn signal, while the left will light with the turn signal and break light.

ANY help would be great as I only have till Friday to get this working.

Burbman · September 21, 2007

How was the vacation?

sonjaab · September 21, 2007

FROZEN...........You also have to remember:

GM changed the wiring pin out in 03. If your using your old plug

in or the same set up from your 01 it won't work with your 04 !

Got to use the old test light to verify !!!!!!!!!!

Flasher module????............Hmmmmm

Sorry about the delay in responding..........Just gor back from Vegas this AM !............geo

How many days till plowing season?????

Jonathan94 · June 26, 2011

Hi - reviving an old thread that covers the exact problem I have, except on the left side.

Did this fix the problem? Is it something I need to have shop do or relatively easy at home? Any part number known?

thanks!

Jonathan94 · June 26, 2011

bit quick on the send - found this other thread that appears to have answered my question.

If anyone has anything more to add though, greatly appreciated!

http://www.gm-trucks.com/forums/index.php?...=94959&st=0

sack1 · July 24, 2011

bit quick on the send - found this other thread that appears to have answered my question.

If anyone has anything more to add though, greatly appreciated!

http://www.gm-trucks.com/forums/index.php?...=94959&st=0

You guys are the best. My '03 2500HD worked fine on the truck but the RR brake light on the trailer plus the pin out on both 7-way receptacles were dead for that brake light, everything else worked fine. In our case I knew it was intermittent since my wife would occasionally mention it when guiding me back

So on the hunch taken from this thread I took the dash fascia off and located the module. Little hard to get it out but with some wiggling it came forth. I noticed too that the cover of the module came off easily and inside is a logic board and open relays. So I replaced it in the socket, by the way, truck lights did not all work with the module out, I tapped on the module cover with a screwdriver and what do you know, the beast inside awakened! It worked!

I still plan to buy a new module, NAPA's is as cheap as anybodies, but perhaps this might be an easy test to see if the module, and probably a relay, is sticking. Give it a few raps on its cover.

Thanks again for all the troubleshooting.

-Rick

KE4HIE · June 12, 2016

I need help with my 2000 Silverado that the left side brake light will not work on the OEM trailer plug.

All lights on the truck work properly. The problen is only with the drivers side brake light on the trailer plug?

I have blinker and emergency flashers on BOTH sides of the trailer plug but only a right brake light.

Being that mine is a 2000 model, it does not have the 10 pin module ( oem # 15764135) behind the fuse box.

it has the tryco # EP-29 flasher module which I have replaced. No change, still no left brake light at trailer.

All fuses under dash and under hood are good. Any suggestions? KE4HIE

Bryanlew · August 11, 2020

On 6/12/2016 at 11:49 AM, KE4HIE said:

I need help with my 2000 Silverado that the left side brake light will not work on the OEM trailer plug.

All lights on the truck work properly. The problen is only with the drivers side brake light on the trailer plug?

I have blinker and emergency flashers on BOTH sides of the trailer plug but only a right brake light.

Being that mine is a 2000 model, it does not have the 10 pin module ( oem # 15764135) behind the fuse box.

it has the tryco # EP-29 flasher module which I have replaced. No change, still no left brake light at trailer.

All fuses under dash and under hood are good. Any suggestions? KE4HIE