brake light malfunction

I have a problem that just appeared with my 97 Sentra.......at all times the right brake/tail light works fine.
When the brake pedal is depressed, the left tail light filament illuminates and not the brake filament. If the tail lights are turned on, the left tail light comes on normal until.......the brake is depressed then the tail light filament goes out and the brake filament remains off.

Bulbs have been replaced/checked out.....both of the tail and brake light fuzes are good......

Any ideas on what the problem is.........is there some kind of brake light relay/solenoid involved?......could the brake light switch cause this?

thanks in advance for any info
dave

there could be so many things wrong that it is hard to tell you what it is. there are some things you can do to narrow the search down though. take a test light or multimeter and see if there is voltage before the plug. then check it at the plug. if there is no voltage at either points a wire could be broke or disconected somewhere. if there is voltage before the plug but not at the plug, you need a new plug. also check on which way the bulb is in the socket, some of those bulbs have the pins in the wrong place and you may not get a conection. another thing that it might be is if you have a bad ground at the harness. follow the wires from the plug and there should be a ground somewhere in the trunk. look for corosion on the wires and in the pug.

i know when we get cars in the shop with probs like this you just have to start at one place and keep moving until you find the prob.

anything else i can do just let me know. i deal with a lot of this stuff so i have seen most everything.