Brake warning lamp on dash 4th gen

Post by **vanzep** » Sun Nov 12, 2023 4:01 pm

My BB1 shows intermittent brake warning lamp on dash.
Some days it lights up and stays on and other days it goes on then goes off when restarting car and some days no warning lamp.
This has being going on/off for some years now.
Fluid levels and brake bulbs all ok.
No issue with brakes or handbrake.

I have seen a few different possibilities for this:

Could be the brake lamp failure box in the rear cluster
or
Could be a fault with the sensor in the brake reservoir cap

Just wondering if any one else has had this issue and info on what fixed it

Scott560 · Post by **Scott560** » Sun Nov 12, 2023 4:54 pm

if your bulbs aren't blown, then my money would be on the level sensor in the cap.

Post by **Merlin** » Mon Nov 13, 2023 8:55 am

On my BB4 I had to ground off the sensor in the rear cluster. Indigolemon did a write up of it somewhere.

Post by **Drax** » Mon Nov 13, 2023 9:16 am

do you have a 3rd rear brake light, one of the oem ones? check that isnt filled with water like mine does....

could be the cause.

otherwise, level sensor in the cap is likely

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Nov 14, 2023 11:10 am

You sure it's not the handbrake switch?

Post by **vanzep** » Tue Nov 14, 2023 4:40 pm

Thanks for the replies/suggestions:

no its the brake lamp warning that is lit up on the dash - the handbrake warning lamp is ok
I checked all bulbs at the rear cluster and the high level 3rd brake lamp (no water in there as i have removed the rear wiper jet from the roof and sealed it up) and they look ok they are dual filament 5w/21w. Also checked fluid level at brake mc reservoir all ok.
Fitted two new bulbs in the rear cluster but warning light persisted but after parking up later on and restarting the car it has gone out (for now). I am expecting it to go back on at some point....not sure about the resistor boxes in the rear cluster - looks like possibly another wire has been added to passenger side cluster- might be something to do with the aftermarket alarm.
Does anyone know the bulb size/designation for the ones in the high level 3rd brake lamp - as they look different. I might fit some new ones as they have never been replaced.

Post by **indigolemon** » Tue Nov 14, 2023 8:27 pm

Hey Nick, been far too long. Hopefully these images help if you want to try and disable the sensor. First two were me testing my theory, second two show the solution. By tapping the plug side it just becomes part of the 'loom' as it were.

Post by **Merlin** » Wed Nov 15, 2023 8:22 am

That's the one! This stopped my brake lamp from coming on.

Post by **vanzep** » Thu Nov 16, 2023 6:59 pm

Thanks G

the dash warning light for brake lamp went on again on start up and went out when restarted once parked up....

Bulbs in rear cluster:
Indicator - Stanley 3497. single filament 21w
Brake Light - Bay 15dP21w/5w dual filament
Reverse Light - 1156 21w single filament

High Level 3rd Brake Lamp:

BU921 - 18w single filament x 2

Post by **Drax** » Fri Nov 17, 2023 9:01 am

shall we add this thread to the tech section?