Steep downgrades, when you need it to control your descent.
Are you talking about the Jake Brake on semis?
not real
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.
at the brake pedal behind or on top
My Chilton Volvo repair manual ( 1970 to 1983 ) shows ( DOT 4 brake fluid )
The 1991 Volvo brake light relay switch is located beneath the drivers side dashboard. The brake light relay switch will be above the brake pedal.
how do you remove the rear brake rotor on a 2000 Volvo v70 awd
DOT ( 4 ) brake fluid , according to my Chilton Volvo ( 1970 - 83 ) repair book
The best way to free a stuck brake on a Volvo is with a caliper spreader. You can find one at an autoparts store or dealer.
Open your hood up and check your brake fluid reservoir.. it should be in the upper right of the engine compartment.. it's not hard to miss... check your level.
you do not adjust the brake lights check the bulbs or check switch top of brake pedal.
It is the same as the brake reservoir. You should see a line heading from that to the clutch master cylinder. Cheers.