Join Date: Sep 2013
Location: South Devon
My Motorhome: Bessacarr E725
Thanked 157 Times in 136 Posts
The gauge is definitely for an air suspension system. It looks to be a simple one where you use an external pump (foot or electric) to pressurise it.
I'm thinking that if you unscrew the brass cap, you'll find a standard schrader type valve to attach the pump. After pressurising, refit the brass cap, and you can press the button to release the pressure.
The idea is to pump the system up for travelling (I use about 3 bar) and then let the air out when leaving the van unused for a lengthy period. No need to let the air out for normal parking. The system helps support the standard suspension and will noticeably reduce roll on roundabouts etc.
No idea what the switch is for, torch and mirror to trace the wiring, I think.
I'm daft and proud of it.