rear light advice need

[daveking]

Hi all
I need to ask about my tail lights.
There is a lower red light and a top
one
on one side the upper is bright and lower one dim.

I have swapped out the bulb but still dim.
I noticed that the socket is a double filament
type.
The bulb can only go in one way.

Thank you.

Dave king

[andrewwynn]

It’s normal. Not sure why but bmw choose to use a high watt lamp driven at low voltage for the run light rather than using the low watt filament.

Extra strange because they used both filament on the other lamp.

The low watt filament has no connection to power it's unused.

If you have one side different from the other side usually from different model bulb or you have something wrong with the wiring.

There's usually some slight difference in the brightness of top n bottom because one is using the low watt filament and one is using high watt but dimmed.

Have somebody hit the brakes while you observe (or take video) it will help explain. You might have mismatched dual filament or somehow have a lamp backwards so the brake filament lit when run filament supposed to be

[daveking]

I was wonderiing why the top has a double filament bulb.as it is not a brake light
And one side is bright,the same brightness as the lower

[andrewwynn]

On my e53 I rewired the lamp so both lights used both filaments and had all four act as run and brake.

On the newer BMW the LCM will adjust the light usage to compensate for burned out lamps so that might be a possibility especially if you attempted to use led lamp which will not dim as meant to be.

With four new lamps they should be similar in brightness but the lower using the low filament and the top dining the high filament.

Something might be wired wrong or bulb model wrong etc.

No light should be bright in the "on" position only the bottom two should be bright when braking.

You can measure the voltage across each lamp in run and brake to root out where the problem is

[andrewwynn]

Take a video including brake application.

Not sure if e53 ever use brake force feedback like e70 does. I have mine programmed to use four lights when ≥ 1/2g braking and have wife's car programmed to engage the hazards if over like 7/10g (I forget the level)

[wpoll]

Originally Posted by andrewwynn

Take a video including brake application.

Not sure if e53 ever use brake force feedback like e70 does. I have mine programmed to use four lights when ≥ 1/2g braking and have wife's car programmed to engage the hazards if over like 7/10g (I forget the level)

The LCI does have "force dependant brake lamps" - not sure about the pre-LCI.



daveking, the dual-filament P21/5W lamps come in three different variations (in terms of base pins) and it's easy to get the wrong type and then get it to "fit".



Not sure what the pre-LCI top lamp should be sorry - maybe inspect the lamp base (and the side that works!).

[andrewwynn]

That’s great feedback that hopefully helps resolve the weirdness


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[EODguy]

Rear fog light is on maybe?

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[wpoll]

Originally Posted by EODguy

Rear fog light is on maybe?

Good thought but rear fog lights are in the tailgate section, next to the reversing lamps.

[EODguy]

Originally Posted by wpoll

Good thought but rear fog lights are in the tailgate section, next to the reversing lamps.

True, but I wasn't sure if it's linked through the top bulb of the brake light since they only come on when the switch is on for rear fog and at least running lights.

Is cross feed even possible?

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