im stumpt? heres the deal my trailer running lights do not work there is no power at trl plugin. also im having wierd things going on in the cab when i turn the right turn sing on my trl brake unit light blinks but if i unplug the unit my air bag off light blinks with turn sing right and left??? HELP
any sugg?

We need the year to help with the problem!:)

Check all your grounds, on the truck and trailer. Alot of trailer manufactures rely on the ball/hitch to make the ground connection from the trailer to the truck and that causes all kinds of weird problems.

My 2004 is having similar trailer lighting problems. I have running lights but the right trailer signal stays solid on. When I signal left, both trailer brake lights blink. The +12v does not have power. It's not the trailer. I used a "Tow Ready 7-Way Tester with LEDs" and the right turn LED constantly stays lit.

This issue just started happening during the summer around the same time I installed a Prodigy brake controller. I bought the plug-in wire harness to install the Prodigy. I have tried unplugging the brake controller and the lighting issues are still there.

im stumpt? heres the deal my trailer running lights do not work there is no power at trl plugin. also im having wierd things going on in the cab when i turn the right turn sing on my trl brake unit light blinks but if i unplug the unit my air bag off light blinks with turn sing right and left??? HELP
any sugg?
Have you checked the fuses in the engine compartment. They have fuses just for the trailer lights in there. Mine did the same thing come to find out the TRL LTS fuse was blown.

my truck is doing almost the same thing now havent figured it out yet!!!

its an 03 and i have checked all fuses and i removed the 2 grounds on drivers side cab monts and cleaned but still no luck but i appriciate all of the sugg.
all are more then welcome i am spinning my wheels on this one

There are different Prodigy wiring harnesses available depending on the year model of the truck. IIRC the change happened after the 2002 model year. Verify the wiring of the Prodigy to your truck wiring.


My 2004 is having similar trailer lighting problems. I have running lights but the right trailer signal stays solid on. When I signal left, both trailer brake lights blink. The +12v does not have power. It's not the trailer. I used a "Tow Ready 7-Way Tester with LEDs" and the right turn LED constantly stays lit.

This issue just started happening during the summer around the same time I installed a Prodigy brake controller. I bought the plug-in wire harness to install the Prodigy. I have tried unplugging the brake controller and the lighting issues are still there.

another problem!!! ok this frickin' thing is drivin me nuts! now when i start my truck every once in awhile the brake light and abs light comes on and message center tells me service brake system????????WTF?? but if i turn the truck off then restart it goes away and all is good?? happened 3 times now at random.

when strange things happen, look for the last thing you did, like I added a brake controller and now my lights are acting stupid, double check brake controller, 01-02 are different from 03-04, pigtail harness should match the year of the truck, bad grounds will cause stupid stuff and there are ground straps in the rear of the frame too, use a good meter and check everything out, I had a new truck that would not supply 12VDC to the plug, dealer replaced harness and problem was solved. Electrical problems are hard to fix sometimes, even more difficult using a keyboard.....

When someone backed into my bumper they detroyed the lid on the plug, Trailer lights wouldn't work right, replaced it and no more problem.

another problem!!! ok this frickin' thing is drivin me nuts! now when i start my truck every once in awhile the brake light and abs light comes on and message center tells me service brake system????????WTF?? but if i turn the truck off then restart it goes away and all is good?? happened 3 times now at random.

Go back and double check the grounds on the driver side mount that you looked at earlier. That is where the ABS/Brake module is grounded. If that ground does not make good connection it will cause the problem you describe. You might should get a star washer to put in there if there is not already one.

I would think the lights should work if I unplugged the Prodigy unless something is now shorted out. The Prodigy was working fine.

I checked all the fuses under the hood and the inside the panel on the left side of the dash. They are all good. I'm lost on this one.

There are different Prodigy wiring harnesses available depending on the year model of the truck. IIRC the change happened after the 2002 model year. Verify the wiring of the Prodigy to your truck wiring.

My 2004 is having similar trailer lighting problems. I have running lights but the right trailer signal stays solid on. When I signal left, both trailer brake lights blink. The +12v does not have power. It's not the trailer. I used a "Tow Ready 7-Way Tester with LEDs" and the right turn LED constantly stays lit.

This issue just started happening during the summer around the same time I installed a Prodigy brake controller. I bought the plug-in wire harness to install the Prodigy. I have tried unplugging the brake controller and the lighting issues are still there.
Search "flasher module". Yours has gone south.

I would disconnect the trailer from the vehicle-- test each terminal in the truck connector-- the connections are stamped on the cover. make sure you also test the ground. That will tell you if the truck is OK!

Then on the trailer with the connection unplugged-- ground the trailer to the truck with a good cable like a jumper cable-- make a hot wire from the truck with a long piece of wire-- test each connection -one at a time-- to see if the trailer corrosponds to the truck plug. make sure you also test the ground on the trailer.

This should help you diagnose the problem.:D Don't take a short cut!

tested plug on truck side all good but tailer running lights also checked plug that the plug goes in to right behind bumper and same thing there

Search "flasher module". Yours has gone south.
Heymccall thank you so much. You were exactly right. Flasher Module.

For everyone else with the same problems here are some pictures.
There is an old (15764135) and a new (10383321) part number. (At least GM realized they had a bad part and were not replacing a defective module with one that will crap out as soon... hopefully.) GMPartsDirect.com has them but shipping is high. My local dealer matched their price plus sales tax. The part should be in the neighborhood of $50 to $60.

The only tool you need is a 7mm socket to remove the 2 screws for the panel under the steering column.

Tilt your steering wheel down. With the engine off and parking brake on, put the gear shift into D. Carefully pull off your dash bezel and set it aside. Put the gear shift back into Park. Remove the two 7mm bolts at the bottom of the panel under the steering column. Pull from the top of the panel and then set the panel aside. Wiggle out the old flasher and push in the new one. Replace the panel bottom first and then the top and then replace the bezel.

As a side note, I did not have turn signals and possibly no brake lights on the truck on the way to the dealer with the old flasher out.

Nice pictures. Good info.

ok i think i fixed part of my problem i cleaned the groung under drivers feet again and repainted and undercoated this time and my service brake message has not appeared for over a week now so im crossing my fingers that i have that solved.

theres a fuse box on the left side of the dash too[when you open the door],it has trailer fuses too