Brake wear lamp behaviour?

[paultv]

My brake wear lamp has been dud for yonks - so being anal I decided to sort it out.

If I disconnect either of the sensors the lamp lights, goes out when all connected - GOOD!

Self test does bugger all.

Is the lamp supposed to light on ignition or on "start" ???

According to the circuits I have here, the self test should only happen when the starter motor
cranks and unloader K5 is released applying 12v to the cluster wear lamp during the starting cycle via an isolation diode on the cluster PC.

Can anyone confirm the usual way this works?

thanks

Paul

[tha881]

I know you may want this feature working, but many and myself included, just remove the bulb from the instruments. In my case, i found that easier than messing about getting those sensors to fit properly in the pads.

[paultv]

Yeah I know - I've had mine dissabled for years - and I don't need a silly light to tell me to change the pads - but its on the car and I thought I'd pay some attention to it.

Turns out it was the solenoid spade connection on the starter motor - its internally broken I guess, so doesn't connecto to the brushes to earth the K5/K7 relays and provide the 12v to illuminate the
check lamp on the dash during cranking.

I jumped the earth connector to the main large brush contact and it now all works as it should - K5 and K7 unload during starting and the check light works too.



Paul

[HJ1981]

I know you may want this feature working, but many and myself included, just remove the bulb from the instruments. In my case, i found that easier than messing about getting those sensors to fit properly in the pads.

My goodness, that is what one of the previous owners did on my E30. I was wondering, why the bulb was missing, despite the brake system getting completely rebuilt and new sensors all round. It should stay on when the ignition is on, then turn off once the engine fires up, then i found this:

https://www.e30zone.net/e30wiki/index.p ... Flickering

Most likely it is the cause of our issues.

[paultv]

My circuit board and that resistor were all fine as it happens - but the whole thing is operated through the solenoid and then the starter motor brushes - if the starter is replaced with a non OEM unit
it wont have the required connector - then come the bodges ending up with removing the bulb out of frustration.

Paul

[ChrisHC]

I tried foe a long time to get mine to work, because I hate having things on the car that do not work, but even with Brian Moore's expert advice I was unsuccessful. My local BMW specialist tells me they were difficult even when the cars were new, and I gave up and took the bulb out, there comes a point sadly to admit defeat.

[HJ1981]

I tried foe a long time to get mine to work, because I hate having things on the car that do not work, but even with Brian Moore's expert advice I was unsuccessful. My local BMW specialist tells me they were difficult even when the cars were new, and I gave up and took the bulb out, there comes a point sadly to admit defeat.

Sad but true

[paultv]

I think there's a misconception about how it should work.

The brake wear light does not light on ignition...it test lights when you crank the starter, then all being well it goes out when the engine starts.

So to fix it you have two states...one with the engine running...you should have no lights meaning the loop from the cluster and back is complete and the resistor in the cluster is good.

Second is the lamp should light on cranking meaning the unloader relays are dropping out and the small wire to the solenoid is making proper contact with the non earthy side of the starter brushes.

A non standard starter will stop it working correctly and a non lit lamp on ignition is not a fault.

Paul