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Garage => Mechanicals => Topic started by: daantjie on 19 June 2022, 10:42 PM

Title: No brake lights
Post by: daantjie on 19 June 2022, 10:42 PM
It never ends...

Seems I lost brake lights all of a sudden :o

Fuse checks out.  All bulbs fine.  Leaves only the switch on the pedal, right?

Is there a test for the switch?  Seems like with pedal at rest the switch is open, then as you press the pedal the trigger opens up and completes the circuit?

Any tips appreciated before I throw a new switch at the problem  ;D

Cheers
Title: Re: No brake lights
Post by: daantjie on 19 June 2022, 11:58 PM
The plot thickens...

I bridged the switch at the harness and I see only left rear brake light on.  Hmm...

Also this brake light only works with ignition in ON.  Not sure if this is right?

I recall reading the cruise control grounds via the brake light bulb(s)?  So maybe I have an issue with cruise control?  I never use cruise control so not sure what is going on here.  I would think that brake lights should override cruise control for safety reasons?
Title: Re: No brake lights
Post by: rumb on 20 June 2022, 09:01 AM
With a meter you should be able to see if the switch is working.
Title: Re: No brake lights
Post by: daantjie on 20 June 2022, 10:15 AM
Quote from: rumb on 20 June 2022, 09:01 AMWith a meter you should be able to see if the switch is working.

Thanks Robert I tested for resistance and it seems to be working in that it goes open with the button pushed in so looks like the switch is good.  Checking all bulbs again, this is reading like a poor contact somewhere.
Title: Re: No brake lights
Post by: rumb on 20 June 2022, 12:48 PM
Always worth checking grounds on any circuit.
Title: Re: No brake lights
Post by: daantjie on 20 June 2022, 07:59 PM
Thanks, I got it going again.  Looks like I had a bad connection on the ground pin on the connector plug and with all my fiddling it started working, soldered it and now works again.

Still odd though that the brake lights only work with ignition ON :-\ ?
Title: Re: No brake lights
Post by: mrkozzy on 21 June 2022, 06:50 AM
Quote from: daantjie on 20 June 2022, 07:59 PMStill odd though that the brake lights only work with ignition ON :-\ ?

I'll confirm that mine is the same.  Ignition "on" brake lights work.  No brake lights without the key being turned.

The tail and head lights work at any time. No key needed. 
Its only the brake, reverse and indicator that need to be powered up.
Title: Re: No brake lights
Post by: daantjie on 21 June 2022, 08:50 AM
Quote from: mrkozzy on 21 June 2022, 06:50 AM
Quote from: daantjie on 20 June 2022, 07:59 PMStill odd though that the brake lights only work with ignition ON :-\ ?

I'll confirm that mine is the same.  Ignition "on" brake lights work.  No brake lights without the key being turned.

The tail and head lights work at any time. No key needed. 
Its only the brake, reverse and indicator that need to be powered up.

Cool thanks  8)
Title: Re: No brake lights
Post by: UTn_boy on 21 June 2022, 03:42 PM
The brake lights coming on only when the ignition is on is something Mercedes has been doing since about 1960.  It's normal. 
Title: Re: No brake lights
Post by: daantjie on 21 June 2022, 04:19 PM
Quote from: UTn_boy on 21 June 2022, 03:42 PMThe brake lights coming on only when the ignition is on is something Mercedes has been doing since about 1960.  It's normal. 

Thanks Aaron good to know cheers.