I have a 1990 l8000 Brazilian 6 cylinder diesel hooked to a BWS air tilt air ramp trailer.The trail gets its air from the red button in the cab ( the red trailer emergency hose at the rear of trailer) The only way to get air to come out the red hose in the rear is to push in the yellow tractor parking brake (release) . Both red and yellow cab buttons must be pushed in ( release) to get air to the trailer tilt. All the brakes are now released unit rolls away. How to I fix this or what Iam I doing wrong