you do not adjust the brake lights check the bulbs or check switch top of brake pedal.
Check wiring for 12v also the brake switch on the brake pedal.
Check the bulbs, check the fuse, check the brake light switch, in that order.
Look under the dash on the driver's side, half way down the brake pedal. When you depress the brake pedal, the pedal moves away from this switch, which allows the brake light pedal circuit to complete, and your brake lights come on. This brake light switch is always hot/on, as required by federal law, so that even with no key in the ignition, if you hit your brake pedal, the brake lights will come on.
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.
If you are referring to the warning light on your instrumentation panel, then you simply need to check all your brake lights, do not forget the center one at the rear glass.
One for brake lights, one for cruise control. If you hit the brakes when using cruise control, that second switch is what tells the control modules that the brake is being depressed.
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I am having the same trouble. My brake lights work with the light switch for nighttime driving, but only far right brake light works when i pres brake pedal. Reverse lights dont work at all. Turn signals and hazard light work.
your headlamp switch on the dashboard has a small screw on it. its a 3 position switch. turn it to switch daytime running lights off.
If the brake lights & horn are on the same fused circuit the most likely cause of the problem is an open circuit before the fuse.
check the switch at the top of the brake peddle.