2008 Nbs Updated Brake Light Switch

Raymond Lowe · November 9, 2008

This past summer, I noticed my trailer brakes cutting out just letting off the brake slightly. It was an annoying thing to happen coming into a corner on a downgrade while your trying to modulate the brakes. Suddenly you've got this trailer pushing you.

Then there was a lengthy thread on the issue in this forum.

http://www.gm-trucks.com/forums/index.php?showtopic=72994

Today, I installed the new switch, p/n 25991704 which was called out in TSB #08-08-42-003. Now, when I lightly touch the brake pedal, the brake lights come on instantly before the rod even begins it's stroke. As you start to ease up on the pedal, the brake lights do stay on longer than before but they will go out before the pedal starts it's travel back up. It's kind of a floating switch that relies totally on contact pressure on the end of the pushrod. This new switch has a "reduced internal spring apply force, which will allow the lamps to stay on with less applied brake force."

The new switch has a white body, the original is all black. The job is about 20-25 minutes and you need a 10mm wrench to take off one bolt on a retaining clip. To remove the old and before you install the new, you have to pop the switches apart. They will only come off or on the shaft in two pieces. My price was around $17.00 but down in the U.S., it's probably around $10-12.

SLESierra · November 9, 2008

should that not of been a warranty item?

redvett · November 9, 2008

You wouldn't see me working on my vehicle with a 4 yr bumper to bumper warranty.

Sir Dan · November 9, 2008

I did take my truck into the dealer for warranty work on the funky brake light thing, but they just stuck in the same poorly designed brake switch, so I took matters into my own hands. There is a thread on here somewhere on how to cut the internal spring in the switch down a few notches so it will work better. This is the only thing that worked for mine. As RaymondT says above, the new switch design is a little better, but still shuts off the lights before your foot comes off the pedal!

Raymond Lowe · November 10, 2008

should that not of been a warranty item?

You wouldn't see me working on my vehicle with a 4 yr bumper to bumper warranty.

For one, I don't to gamble on which rookie gets to work on my truck. For another, it does not neccessarily qualify as a defective part and you might not get it covered under warranty. And most importantly, my time is worth something. I'm not going through the hassle of making an appointment, dropping the truck off, waiting for a phone call, driving all the way back to pick up my truck to find out they had to order the part, etc, etc, etc...

Hell, even if it was $50 bucks I still would pay it just to avoid that kind of extreme grief.

kdogg · November 11, 2008

I just wnt to get this straight. The light turning off too early releases the trailer break before the actual truck break and smashes the toung of the trailer into the ball hitch? Just asking, because I always thought this to be true, but still thinking there was something wrong with the toung hitch connection. So if I'm reading this right. The new switch works better? So now it will feel like a small car hitting the back of the trailer instead of a small truck? I don't understand how this little switch turned into such a big flaw! I would never suggest altering the design even though flawed possibly turning liability of a major accident to myself.

Raymond Lowe · November 11, 2008

I just wnt to get this straight. The light turning off too early releases the trailer break before the actual truck break and smashes the toung of the trailer into the ball hitch? Just asking, because I always thought this to be true, but still thinking there was something wrong with the toung hitch connection. So if I'm reading this right. The new switch works better? So now it will feel like a small car hitting the back of the trailer instead of a small truck? I don't understand how this little switch turned into such a big flaw! I would never suggest altering the design even though flawed possibly turning liability of a major accident to myself.

Electric brake controllers actuate the brakes from the brake light circuit. If your brake lights go out, the trailer brakes come off. Then you get the weight of the trailer pushing onto the tow vehicle coming down the hill. You can "feel" the weight of the trailer coming to bear. You may have some play in your setup giving you that feeling of something hitting you. I have a dual-cam equalizer and you can't feel any movement or clunking between the trailer and truck when you brake.

The problem with GM's switch is that it has actuates on pedal pressure, not pedal position. The whole switch actually moves with the pushrod when you apply the brake. When all of us use our brakes, we modulate the pedal without thinking about it. As our brain decides we are slowing down too fast, we ease up on the pedal slightly to reduce the braking effort but we are still braking. GM's original switch with it's stronger spring can trip the brake lights off even though you are still lightly braking. That releases the trailer brakes and suddenly you get the extra weight pushing you. On the level, you might hardly notice anything. On a 6% down-grade, it will definitely get your attention.

I'm sure it will help as the brake lights come on with the slightest foot pressure but I won't know for sure until late spring when I get the trailer out again.

asilverblazer · November 11, 2008

The problem with GM's switch is that it has actuates on pedal pressure, not pedal position. The whole switch actually moves with the pushrod when you apply the brake. When all of us use our brakes, we modulate the pedal without thinking about it. As our brain decides we are slowing down too fast, we ease up on the pedal slightly to reduce the braking effort but we are still braking. GM's original switch with it's stronger spring can trip the brake lights off even though you are still lightly braking. That releases the trailer brakes and suddenly you get the extra weight pushing you. On the level, you might hardly notice anything. On a 6% down-grade, it will definitely get your attention.

I agree.

brims · March 25, 2009

I did take my truck into the dealer for warranty work on the funky brake light thing, but they just stuck in the same poorly designed brake switch, so I took matters into my own hands. There is a thread on here somewhere on how to cut the internal spring in the switch down a few notches so it will work better. This is the only thing that worked for mine. As RaymondT says above, the new switch design is a little better, but still shuts off the lights before your foot comes off the pedal!

I know this is an old thread, but importatnt. Do you happen to know which thread talks about the modification? I'm searching this forum using google and have yet to come up with it. I'm deep into the search results with nothing matching this fix (14 pages in).

Ranger · April 16, 2009

I'm having trouble figuring out how the switch is supposed to come off...The retaining clip won't disconnect and don't want to disassemble the switches without knowing for sure it won't f up some calibration.

msinawsk · April 17, 2009

does this tsb really work or not???? seems to be mixed results..!

scottmoyer · April 17, 2009

I experienced this with my trailer. I loaned the trailer to a friend one weekend and he had the same issue with his Tahoe. Another friend used it and had the same problem with his Silverado. These 2 friends have pulled other trailers without issue so I assumed it was my trailer. Why does it happen on some trailers but not others? The trailer was purchased from a Dodge owner and he never experienced this. I sold the trailer so I can't test again after a new switch install. i would like to know how to permanently fix this issue as I believe my family's safety is at risk when I trailer my car behind the truck.