GMC Sierra parking brake light stays on

We have a 2001 GMC Sierra 4.8L 1/2 ton 2WD that we use to tow sometimes. The parking brake light is staying on. I put new shoes on it, they're adjusted correctly and hold tight, and also replaced the electrical switch under the dash that is connected to the actuating foot pedal. Light is still on. Took it to the GM garage (which we never do and goes against everything in me) and after two days they can't figure it out either.

The weird thing to me is that the last time we towed it came on instantly after I disconnected the trailer wire from the plug in the back. ??? I don't know how but I'm thinking it has something to do with the trailering wire and/or brake controller (all of which works fine).

Anyone have any ideas what it could be? Is there a way to disconnect it? We have state inspections in Texas and ours is up next month and I'm not sure if it will pass with the light on even if the parking brake works fine.

Thanks.

[Rob Petrie E395]

Is the pedal coming all the way back up when its released. Try pulling the release handle and pull up on the pedal at the same time. I just had one in my shop where the plastic cover got deformed and got in the way of letting it back up all the way. I clipped a small piece of plastic off of it and it was good to go.

No, that didn't cure it. Thanks for taking the time to respond though. Here's something interesting I just noticed. When you engage the parking brake by pushing the pedal down the parking brake light on the dash blinks. When you release the pedal and the parking brake is off the light stays on solid and doesn't blink. ???

[magnumv8]

If the e- brake switch has 1 wire on it then all the light is looking for is a ground so the light will come on.....so with the wire disconnected from the switch the light will not come on...if removed from the switch and the light stays on, there is a short somewhere between the switch and the light itself....

If there is 2 wires on the switch that usually means the e-brake is being monitored by a BCM (body control module). In which case the BCM is just looking for continuity through the switch to tell it the e-brake is engaged. This makes it a little tougher to diagnose since the BCM controls the light (it can also control and monitor all the systems in the vehicle depending on how new it is). Any spike in the electrical system can cause the BCM,ECU or Dash cluster to fail. Something as simple as plugging in your trailer plug or a problem in the trailer wiring can wreck havoc on the vehicles electrical system.

I don't recommend plugging trailers into a tow vehicle anymore that has the engine running, plus one other thing, manufacturers require us to disconnect every electrical connection to these items plus the batteries and any other monitored piece of equipment on the vehicle before welding on it......

Sorry for the long response (plus a little off track)....

D L Rambo.....Stk1300

Went to pick up the trailer today because we have to dyno tune tomorrow and when we plugged the trailer into the truck (the truck was off) the e-brake light is still on. When we got home I unplugged the ONE wire going to the switch under the dash and the light is still on. Any suggestions what to do? Brakes are working fine on the truck, fluid level is correct, e-brakes on the truck work perfectly, trailer lighting and electric brakes on the trailer are good, ... This is getting a little frustrating.

[magnumv8]

I just finished reading the diagnostic repair procedure for your issue and I am afraid your only choice for repair is to go through a repair facility that has the proper scan tool to diagnose your problem....your truck apparently does have the BCM module and it monitors all of the brake systems, so your issue could be anywhere from a short to a bad switch, sensor or BCM.....the repair sequence has 14 separate steps to diagnose the problem and unfortunately you need the proper scan tool to do it.....

D L Rambo Stk1300