lmtv 1078a1 brake lights stay on!!!

[ironlung80]

when you turn on the truck and air preasure builds up brake lights come on and stay on.

does anyone know what the cause of this issue could be?

 

[Scar59]

A little trouble shooting will help; are the brakes actually engaged? Treadle valve (brake pedal) bypassing (hissing)? Find the brake light switch and meter it out. Most likely the pressure switch.

 

[ironlung80]

no hissing, grounds are good on the brake lights, changed the light switch out

 

[ironlung80]

no hissing, grounds are good on the brake lights, changed the light switch out

 

[Scar59]

Did the switch replacement fix the discrepancy?

 

[Suprman]

On the treadle valve are two round pressure switches they control the brakes. I believe there is a relay involved also.

 

[ironlung80]

ok will look at treadle valve next

 

[Suprman]

Air could be leaking thru but I would check the switches and wiring. You can use an ohm meter and see when the switches close with the pedal depressed or with air pressure.

 

[Gunzy]

Does the truck have a trailer brake handle? If so make sure it isn't applied, even slight application will turn the brake lights on.