2016 W900 Brake lights staying on.....

If you pull your blue gladhand off the trailer, is there air?

 

If the pedal is sticking WD 40 won’t work like PB Blaster. The PB Cleans the dirt and grime out like WD 40 won’t do. If your pedal is not sticking this won’t help, but there really is a huge difference in PB Blaster and WD40.

 

If there is air, see if it's coming out of the blue line, or out of the trailer gladhand.

 

Ok. Has that application gauge shown pressure since this started, or has it always?

I'm going to figure you'd know if your brakes were dragging, especially 80 psi