Are you talking about the Jake Brake on semis?
Usually busses do not have retarders because they are too loud and cannot be used inside most city limits on a semi truck they have a switch to turn on the jake brake (engine brake, or retarder) when the switch is on and you let the accelerator all the way up the brake takes over. All a retarder does is use your air brakes (or hydraulic) less to prevent overheating that will lead to brake loss.
Steep downgrades, when you need it to control your descent.
a retarder shouldn't be using an automobile in the first place
no it do not answer my question
If none of the brake lights are working i would suspect the brake switch at the brake pedal.
No
the brake light driver side not working
probably the brake light switch on the pedal if none are working at all
Bulbs blown, or corroded sockets.
It slows down the drying time
fsa