Hi have a Audi a8 rear n/s brake led light can it be replaced or will have to replace the hole circuit board.

SOURCE: Replace brake pad light on, how do you reset it?

Did you change the sensors when you changed the pads?

SOURCE: 98 Suburban Brake and hazard lights don't work

Check for power and ground at the two panel lights. GM uses a cheep circuit board design, they overheat and corrode on the other side of the board. not serviceable.

SOURCE: Audi A4 need to replace rear brake light on audi a4

Inside the boot is a plastic cap embeded in the boot liner. Remove the cap to reveal a screw. Undo the screw and the whole rear light cluster will come away in a sideways and not rearward direction to reveal all of the bulbs. Hope this helps.

SOURCE: how to replace rear brake light bulb on audi a4

More than likely you will need to remove the entire tail light assembly from the inside of the trunk. You should see some twist knobs under the trunk liner or exposed.

SOURCE: Audi A6 2005 LH Rear Turn Signal & Brake Light Failure

I had a problem with rear left side signal brake and reversing lamps not working on my 2007 A6 2.L Tdi SE.( Intermittent fault for 2 months)
I think I have identified the problem.
The seal between the Lens and the bulb plate had allowed moisture into the lamp.
During sunny days the water evaporates and enters the multi pin connector at the rear of the lamp.
On close examination of the connector I noticed minor discolouring of the ground ( Heavy Brown Wire connector Causing intermitting lamp failure )
SOLUTION
I expelled all moisture from the lamp and multi-pin connector.
I removed the neoprene seal from the lamp and refitted it good side up
I cleaned the ground pin on the connector with 600 grade paper and contact cleaner
I put a slight twist in this pin with long nose pliers so as to get better connection.
Lamp is working fine since.
Changing the bulb plate may also work
Great care must be taken when changing bulbs or this problem will reoccur