Why does my rear light go out when I press the brakes?

[simon tarr]

And only on one side.

Answers on a postcard please.

[marshman]

Faulty earth wire connection to the light unit on that side.,I would assume your indicatpr light on that side has a similar effect.

Roger

[stag-phil]

One possible cause is the bulb has been put in incorrectly.

Take the bulb out and make sure the two lugs are correctly aligned.

Phil

[simon tarr]

Hi Roger,
Have not tried indicator with running lights. Will check that out.

So if a faulty earth, can you explain why the brake light has that effect? And how do I fix it?

Thanks Simon.

[jleyton]

I'd put a large sum on a bad earth

Cheers

Julian

[Kevin Garrod]

I would start with a new bulb, sometimes when they fail one filament breaks and makes contact with the other causing the symptoms you describe.

[Motorcycle mad]

Hi Roger,
Have not tried indicator with running lights. Will check that out.

So if a faulty earth, can you explain why the brake light has that effect? And how do I fix it?

Thanks Simon.

Hi Simon

With a faulty earth on your rear/stop lamp, (say your near side for this illustration), this bulb finds an earth route via the stop lamp filament of the nearside bulb (the same bulb, being double filament), then back along the wire to the offside stop lamp (both bulbs being wired in parallel) and earths through that bulb. When you apply your brakes, positive supply is fed to both stop lamps, which in effect puts a positive supply on both sides of the nearside rear/stop lamp bulb, this means no currant flow, therefore no light.

Remedy as suggested in other threads, i.e. new bulb holders, clean up bulb holders, clean bulbs, put earth wire on lamp(s), solder earth wire direct to bulb holder.

Best of luck

Ken

[simon tarr]

Hi Ken,

Clear and excellent description, many thanks.

Will have a go tomorrow and fingers crossed.

I suspect that I have disturbed something as I have only just revamped both rear light clusters.

Broke down 2 weekends ago, when the boot flooded with petrol! Luckily it all drained out through an unplugged hole in the boot onto the nice hot exhaust, useful design feature?
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Turned out to be a faulty washer on the fuel pump air chamber, excellent service from SU Carburettors, £4 of parts and 30 minutes later all fixed.
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As I had the boot stripped out I decided it was time to sort out the rear lights, as the foam gaskets had all but completely disintegrated, so out they came. 2 weeks, lots of chrome polish, some shiny sticky backed Aluminium tape for the reflectors and 2 new foam gaskets (thanks Rimmer Bros) later all was well.
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Well? Well until, that is a friendly taxi flagged me down on the way home to let me know that my light was going out every time I hit the brakes!!!!

Anyway, that's Sunday all mapped out for me now.

Thanks for all the help everyone.