I assume that this is on once you start the car up but mine only comes on when you switch the sidelights or mainlights on,......and when you brake !!, as i'm a mechanical novice i'm looking firstly at an easy solution such as a bad earth, but could you lads give me some more advice.
Many thanks in advance .

 

The back lighting comes on with the sidelights, whether or not the engine is running, it's wired into the same position as the sidelights.
tabetha

 

You've got the wrong tail / brake light bulbs fitted, or they're fitted incorrectly.

What car by the way?

 

I have a Focus 1.8 LX hatchback, 03 reg, i did change a rear brake light bulb a few weeks ago but cannot remember whether the problem stems from that .

 

That will be your problem, guarantee it! Remove the bulb and see if it still does it.

 

I used an RW382 which caused the problem, on your advice i went to a motor spares shop and she gave me an RW 380 double filament bulb, problem solved, thanks very much .
Backlighting, mine comes on only when i turn on the lights, car running or not, is this correct .

 

Yes that's right, dash lights will only come on when you switch the lights on.

 

Thanks .