66vetteman

As a follow up, I changed the other rear socket and the problem is gone! Thanks to Doug and oldscsc for all the help.

No trailer light kit. It is a van conversion so it has lots of interior lighting, rear stereo & spkrs, TV, elec couch/bed etc. This was all professionally done well before I bought it. The brake light problem is recent as there is a yearly safety inspection where it was discovered. Not found last year.

With park or headlights ON: both bulbs light the dimmer filament. When brake is pushed the bulb with the new socket lights the bright filament and the dim filament, the other light goes out. With park or headlight OFF and brake pushed: The bulb with new socket lights the bright filament, the other one lights the dim filament.

I was able to find only one socket so I replaced the one I thought most likely to be the culprit. Now the brake light with the new socket works and the other one doesn't when the headlights are turned on. In fact it is dimmer than before when the brakes are on with the headlights off. Does this make sense? I have another socket on order, be here Monday. Interesting findings when shopping for a tail light socket. GM only services the tailight harness, $111.82 for each side. NAPA had the socket only with wire pigtails for $24.85. They also have the harness assy for $18.52 per side. So the harness assy which has 3 sockets, wire harness and connector to plug into the main harness is LESS than the socket only and over $93 LESS than GM. ??????

Put the fuse back in and pulled all the bulbs, one at a time, replacing the previous one before pulling the next. Brake light did not work when the headlights were turned on.

I pulled the fuse for the parking lights and the brake lights now WORK with the headlights on. The fuse controls the lic plate, tail, park, fr side markers, glove box & ash tray lights. Bad socket in one of these locations and/or can it be a bad ground as well? I didn't replace the side mkr bulbs but I will. This van has a total of 4 rear lights, two on each side. The top lights are the running/turn (2057), the bottom are the running/brake (1157). All 4 are dual filament.

I will give that a try tomorrow. Getting cold and windy here and have to work outside. Thanks for all the help, I appreciate it!

I unplugged the headlights and the problem continues.

Can I disconnect the headlights one at a time, it is easier than removing the bulbs as I would have to remove the battery to get at the pass side one?

I just changed all the bulbs, even the front running/signals. One of the front signal bulbs twisted off in my hand so they needed to be changed anyway. Though it might have been the problem but no luck. Thanks for the info on the brake sw & fuse. Any other thoughts or ideas?

2000 Chevy Express Van 1500, 5.7L. Brake lights work fine until the headlights are turned on. When the headlights are turned on and the brake applied, the bottom running lights (same bulb as brake lights, different filament) go out and the brake lights do not come on. Third brake light works ok regardless. Any thoughts? Thanks!