Need help with brake light on 1991 Mazda 323

I have one brake light not working, bulb is brand new, electrical looks fine, what could be the problem?

Asked by for the 1991 Mazda 323
used a test light check for juice at the socket of the bulb, make sure you have a good ground.
ground is good, and juice is going to all but one bulb?
1 more answer
Check and clean the soldered contacts and the body ground of your bulb socket. Make sure the contacts are touching with the bulb.