brake / Tail lights stay on, help please

as I remember there is a pressure switch on valve, under the hood... it is not hidden like on Volvo FH....

 

On a KW it's probably behind the dash panel (one of them) screwed into a big aluminum block with several other fittings. It will have 2 wires coming off of it of a pretty heavy gauge. There might be several and it probably looks like this.

 

check them for operation with a multimeter, and if one needs replaced, check to be sure you get one that is the same, as there are normaly open and normaly closed...


found that out when a #### mechanic swapped in the wrong one... LOL

check that the valve block is exhausting properly too.. my current POS doesnt exhaust properly all the time, so it holds on the brake lights.

 

If it has been sitting, the air switch is just probably rusted and now stuck. Still need to replace it.
***Actually, I just remembered, the brake pedal may not be fully up either. This is common too with trucks that have sat for a long time for the brake pedal to get sticky. Grab the pedal with your hand and make sure it is all the way up.

 

I have had issues with the metal cylinder under the brake pedal that goes over plunger of footvalve getting tight and sticking. Check that and clean it,only takes a little dirt or rust to keep it from fully releasing pedal.

 

Pull the floormat out from under the pedal.

 

The plunger in the pedal can corrode and stop the pedal from returning. The best way to test if it is a switch or a foot pedal or trailer valve is to drain all the air from the truck every last drop. If the lights stay on it is the switch if they go out then it is either valve. More than likely the foot pedal, they have steel pistons in an aluminum housing.

 

Just to rule out something, you're still bobtail right? The reason I ask is I had a short in my trailer one time that caused this issue. Other than that I have seen both the pressure switch and a sticking pedal cause this like previously mentioned.

Good luck.