Your B-D exhaust brake/retarder
works by closing a butteryfly valve in the exhaust pipe just downstream from the turbocharger. This causes back-pressure in the engine, which slows the vehicle. That switch turn on the electric side of the unit.
When you turn it on, nothing happens unless you are moving over approx. 25 MPH, then the valve closes and you feel the MH slowing.
The BD link explains everything.
I know nothing of the other issue.
2000 Winnebago Ultimate Freedom USQ40JD,
ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy