I'm a bit stuck with my Fiesta. When I have the lights on, the brake light on the passenger side isn't lighting up.

I changed the bulb today, and with the cover off, when I hit the pedal it does get brighter but not very much.

With the cover on its barely noticable so when its dark and the rear lights are on it looks like the brake light is out completely.

Its trying to light up but not really working. I'm using a Lucas 380 dual filament bulb 12V 21W which looks right. This is a newish problem that I only noticed a couple of weeks ago.

I've checked a couple of bulbs and a couple of fuses. Any idea what else might be causing it?

I doubt its the brake switch as its only one of them.

In the meantime I am going to try and sort the top brake light so I at least have 2. Thats a problem in itself!

Sounds like a bad bad earth, do any other bulbs light up at all when the brake pedal is pressed?

Thanks!

Not that I know of, I have had someone check with it parked up and all the lights on and it all looks normal. The fog and reverse lights look right. I did have a bloke flashing me down the motorway last week (I wasn't braking) but I got home and checked it andthe rest all looks normal so I am presuming he just wanted me to pull over so he could mug me.

How do I go about checking the earth?

you need to find the earth point, and disconnect it and touch a new bare metal part, if its an earth issue then a temp new earth point should stop the issue. if its a wiring issue, then the problem will still happen

Thanks for helping with this, I popped into my garage this morning for something else and mentioned it and he said it looked like the bulb was the wrong way around. He was right and I fixed it earlier.

Thanks again

Never heard of it being the wrong way round only lighting it up a little bit! but its useful information!

I think you should mark your answer above as the resolved! :D

The pins on BA15d 5W/21W 380 bulbs are at slightly different heights to prevent this.

However, I can see how they could still be inserted the wrong way around and then pushed in far enough for the just the lower pin to engage.