Brake lights don't work when headlights are on!

Doug_Scott · March 24, 2012

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. ??????

You may find you have the socket connected backwards. The bulb has two filaments, one brighter than the other. Parking light is the dim filament.

66vetteman · March 24, 2012

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.

Doug_Scott · March 25, 2012

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 think you have found the bad socket then. Has this truck had any modifications to the wiring that you know of? Like maybe someone installed the U-Haul trailer light kit?

66vetteman · March 25, 2012

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.

66vetteman · April 2, 2012

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

Morgan1986 · April 2, 2012

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

what do you guys mean when you say rear socket ?

oldscsc · April 2, 2012

Good to hear you got it figured out!

txab · April 2, 2012

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

what do you guys mean when you say rear socket ?

The light socket that holds the bulb. Duh!

94chevysilv · November 10, 2013

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

This same issue is happening to my 1994 Chevy truck. I replaced the circuit board for both sides, and still doing the same. You said you replaced the rear socket. Can you upload a picture of how it should look?

gmtech4 · November 10, 2013

This same issue is happening to my 1994 Chevy truck. I replaced the circuit board for both sides, and still doing the same. You said you replaced the rear socket. Can you upload a picture of how it should look?

please refer to post #23 for your answer

jozzb · March 31, 2014

Identical symptoms on my 2000 Chevy Express 2500 van, although only on one side. Upon inspection, the back up lamp and socket were very corroded, and although the lamp was still functional, I decided to replace the tail light harness and lamp for less than $30 at the local auto parts store. This solved the brake light problem as well. I thoroughly appreciate the generous expert contributions on this thread which helped me save a trip to the mechanic.

Drewniverse · August 15, 2019

YESSSSSSS!!!!!! I know this thread is several years old but........

Same exact problems on 1998 GMC Savana 1500. Brake lights work with headlights off; brake lights turn off with headlights on.

I bought one socket for the right side and changed it out today. IT WORKED! Just ordered the socket for the left side and I'll install it tomorrow.

Thank you guys!

Jesse Sim · July 7, 2021

Not to take over this discussion, but i am having the same issue, however, when i disconnect the front parking lamp fuse, i have brake lights and tail lights. Im not horribly experienced with wiring but i am learning. Could you refer me where to look?

Thanks in advance!