Brake Lights Won't Turn off

You can try the brake application pressure sensor switch. On new W9 and T800 plus T660 it is behind dash gauge panel below light switches. Factory part #Q21-1041. Amazon lists it for PACCAR, Volvo, Freightshaker.
$351 from dealer or $89 from Fleetpride if you need it next day. Amazon has them for $18.97 but shipping from California so it may take a week to get to you.

Big thanks to JoshK85 for the info and Amazon link.

 

Replaced the valve and still doing the same thing. First time I started it the lights were on, drained all the air they went out. Started it again filled up the tanks lights came on so I drained them and they wouldn't go off so I had to unplug them and get some sleep, but I'm so baffled about this I can't sleep!

 

Freightliner has a campaign to replace the brake switch.

They were crapping out internally.

FTL FL863A CAMPAIGN -BUL#10-442 CASCADIA BRAKE LIGHT ILLUMINATION

 

2000 w900 brake lights staying on tried 3 new brake light switches and 2 new blinker control arms took the signal fuse out and stop light fuses I checked for power at the box with out the fuse in and have power on both sides I need help please.

 

Short to power somewhere after the fuse by the sounds of it.