2015 389 Peterbilt

You mean just by disconnecting the batteries?

 

You should have a master disconnect. Some trucks don't have them, Then yea disconnect the power.

 

Sure it could. Watch for the lights to go out while unplugged. If the sensor is reading pressure the CECU will leave the brake lights on if it shows pressure(which may not be there). With no way to monitor you will be left with swapping parts. Otherwise, take it in. I would check both brake application and service brake lamp switch. the gauge stuck at 50 is what is leading us to application transducer.

 

Ok. I disconnected the brake switch earlier and with both wires taken off it still left the brake lights on. I will look for the other switch and get back to you.

 

Alright. I met up with the driver and swapped the brake applied transducer with the secondary air transducer. The brake lights seem to be acting fine now, and lo and behold the secondary air pressure is reading 150! So it would definitely appear that the transducer was the problem. I appreciate your help very much and hopefully that was all there was to it. Thanks again, guys!