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Old 27th September 2019, 09:04   #11
Odd Job
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Would a blown fuse make the light stay on?

Sorry if that's a dumb question, I'm still trying to get my head around the CANBUS system.
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Old 27th September 2019, 10:21   #12
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Would a blown fuse make the light stay on?
Richard; the reason for the suggestion that you check fuse 13 (in the passenger compartment fusebox) is that it is a 12v supply to the Light Switch Module (LSM), as is fuse 25. The LSM controls all exterior lighting including the brake lights. It is therefore possible that, if either of these 12v supplies is missing, the LSM could enter a fail-safe mode and illuminate the brake lights continuously.

However, you have reported that on arrival at work the brake lights had reverted to normal operation. This might indicate an intermittent fault.

Please check these two fuses, numbers 13 and 25, and I also have two questions for you:
  • Are all 3 brake lights illuminated or just some of them?
  • Is the brightness of the brake lamps normal or at the lower level associated with a tail lamp?

You need not worry about the CAN bus because it isn't involved in brake light operation.

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Old 27th September 2019, 11:43   #13
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Not sure if you are aware, but remember that if your rear side lights ( parking light whatever the correct name is) are out the brake lights will switch on at 50% brightness. You will have a bulb out warning light on your dash if these lights are out though.

Are your parking lights at the rear working ok?

I've found mine to fail intermittently, sorted it out though with some contact cleaner at the rear light plug.
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Old 27th September 2019, 11:55   #14
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.. if your rear side lights ( parking light whatever the correct name is) ....
As you've asked Haydn, I'd suggest that a clear and simple term is the historical one: tail lights.

Simon
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Old 27th September 2019, 12:29   #15
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Quote:
Originally Posted by SD1too View Post
Richard; the reason for the suggestion that you check fuse 13 (in the passenger compartment fusebox) is that it is a 12v supply to the Light Switch Module (LSM), as is fuse 25. The LSM controls all exterior lighting including the brake lights. It is therefore possible that, if either of these 12v supplies is missing, the LSM could enter a fail-safe mode and illuminate the brake lights continuously.

However, you have reported that on arrival at work the brake lights had reverted to normal operation. This might indicate an intermittent fault.

Please check these two fuses, numbers 13 and 25, and I also have two questions for you:
  • Are all 3 brake lights illuminated or just some of them?
  • Is the brightness of the brake lamps normal or at the lower level associated with a tail lamp?

You need not worry about the CAN bus because it isn't involved in brake light operation.

Simon
I cant find any fuses blown.

When the lights were on, all 3 stop lamps were the "normal" brightness as if the switch was activated.
I checked all the other lights and everything else was working fine.

I've checked twice a day since it happened and so far, all good.

Richard
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Old 27th September 2019, 13:37   #16
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Thanks for your reply Richard. Until the fault recurs there's not a lot you can do. I think you're going to need the services of a multimeter though, starting with the brake pedal switch.

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Old 27th September 2019, 13:48   #17
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I had similar problems two or three years ago. Brake lights would go ok for a week or so then stick on, reset brake light switch then ok for a while but eventually got worse.

A new brake light switch from Rimmers cured the problem in the end, but not a nice job to do. Also, only get the switch from Rimmers, eBay ones do not work.
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Old 27th September 2019, 13:54   #18
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Quote:
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As you've asked Haydn, I'd suggest that a clear and simple term is the historical one: tail lights.

Simon
Until you are actually parked on an unlit road with a speed greater than 30MPH in which case you have to leave "parking lights" on - seems to be a very little known feature that when you switch the ignition of with the indicator Up or Down then that side's side and tail light illuminate - hence the P on the indicator stalk.
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Old 27th September 2019, 14:03   #19
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... to leave "parking lights" on ...
Thanks for reminding us of this feature Kelvin. As you say, it utilises the side and tail lamps on only one side of the vehicle for a specific purpose.

I can't remember the last time I parked on an unlit road with a speed limit greater than 30 mph. It sounds a scary practice in this age.

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Old 27th September 2019, 14:19   #20
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Quote:
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Until you are actually parked on an unlit road with a speed greater than 30MPH in which case you have to leave "parking lights" on
If lights are required when parked, both front and both rear position lamps are required to be on (not just one side) - reg.24, The Road Vehicles Lighting Regulations 1989.
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