Brake light only work when all lights are on
 

Hey there. New here, sorry if I'm violating any rules but I've done a lot of Googling and come up short, so I signed up to this forum.

My girlfriend has a 2003 Civic. Her right brake light does work but ONLY when all lights are turned on via the indicator stalk.

So I know it's not the bulb, socket, fuse or wires because the light does work but only when all lights are on, like how you'd run them at night. The bulb has also been recently replaced.

I feel like it could be a relay issue but I know very little about them and would appreciate some insight. I bought her a Hayne's manual but of course it's more DIY fixes than troubleshooting.
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Re: Brake light only work when all lights are on
 

Are you sure you are looking at the brake light, or are you looking at the marker light?

Both are in the same place as it is a dual bulb.

Try this; do the same thing you did and make sure you ask your girlfriend to step on and off the brake. If you do not see it change in brightness then you are looking at the marker light.

if so replace both bulbs.