number plate lights go off with brake lights

[muttleypup]

A little while ago i fitted LED units to replace u/s number plate lights (lenses were cracked/misted and terminals shot) and all seemed OK. the feed to the number plate bulbs has been taken from a live to the left hand rear light cluster, the original feed having gone dead and couldn't find the cause. However, as i now find out, every time the brake lights come on the number plate lamps go out! Anyone got ideas as to why?

Not a major issue i guess but going to bug me now i know about it

[marlinowner]

Sounds like an earth problem, if the left hand rear cluster loses its earth, those lights will earth through the brake light bulbs to the other side - when the brake lights are on this won't work and the rear lights will go off.

[muttleypup]

Thanks for the response, excuse my ignorance but electrickery not my thing, why would this only affect the number plate lamps? Wouldn't it knock out the tail lights as well? Obviously need to check the earth crown but just trying to understand

[marlinowner]

Yes I'm trying and failing to understand quite what is going on, I think it's something to do with earthing and the fact that the brake lights are connected together, unlike the tail lights, but my brain hurts if I try to pin it down further...

[muttleypup]

Ha OK yes makes my head hurt, i'll have a look at the weekend and see if i can find out a bit more, cheers

[marlinowner]

It occurs to me that if you wired in the led lights with a new earth connection, and accidentally connected that to the brake light supply, it would behave as you describe. A big if though.

[muttleypup]

basically what i was thinking based on your original answer, just try an 'isolated' earth and see if they behave properly. i'll post any results when i get chance to look at it in between ripping the kitchen out at home

[muttleypup]

When run to an isolated earth it all worked as it should. Problem seemed to be the o/s lamp cluster. If i pressed the brake light bulb, it went out and number plate lights came on. Same effect when wiggling the connector on the back, much pressing, cleaning and fiddling later and now have no brake lights either side! Fuse is fine. Think i may have to source another rear o/s light to solve this unless anyone has any suggestions

[Oldiebut goodie]

Check, and most probably replace, the light cluster earths each side and I should think that normal service will be resumed.

[muttleypup]

Well cleaned up all connections including the earth crown and sorted iffy live feed to o/s brake light. That got me back to where i was to start with. After more fiddling and testing earths/lives with a small test bulb i'm none the wiser so have for now run an earth feed for the number plate lights to light cluster body mount and it all works 'as it should'. a job for another day i think, when my patience returns

[Oldiebut goodie]

Earth crowns are the wrong end of the van - have you cleaned the earth point on the nearside bulkhead in the engine bay?

[muttleypup]

Ah!! No Thanks for the heads-up I'll have a go at it tomorrow hopefully and see if that solves the problem. I did say electrickery wasn't my thing