tail lights and stop lights go out when brakes applied

[wayne petty]

some tips and how it is supposed to work.

i have run across this a bunch of times.

when the headlights are on.. and you step on the brakes. half the tail lights quit completely.. and the brake lights on that side don't work either..

this side will also have dim tail lights..

depending on how the sockets are grounded..  and where the broken ground connection is.. you could have some weird operation..

this is looking down into a tail light socket with both tail and turn/stop circuits..

note that the  circular shell holds and actually grounds the bulb.. but.. its grounded only thru the tail light housing.. if its not secure.. or the tail light housing is poorly grounded. you will have issues.. drop to the bottom of this first section for a fix that can be for testing.. temporary or forever..




this is a side view.. so you get a better idea of what you are looking at..



the white colored version.. this is a mid to late 60s gm tail light socket..  that there is a hole at the 8 o clock position..

a similar opening on the black version at the same 8 o clock position.. more on that later..

lets look at standardized mid 60 to mid 70s tail light and side marker light wiring..

note that the stop/tail light bulbs are grounded by the shell..  the side marker lights are individually grounded .




this is how mid 70s thru late 90s  tail lights are wired..

less my splices..



converting the side marker light wiring to this set up makes the side marker lights flash out of phase.. with the turn signals... and still maintain the bulbs showing when the tail lights are on without the turn signal lights flashing..

so.. back to the original title..

tail lights go out when you step on the brakes or operate the turn signals...

strip back several inches of 16 or 18 gauge wire.. loop it around and reinsert the bulb into the socket.. then feed the new ground wire thru the hole at 8 o clock as shown way above..  once the bulb and socket are back in the housing.. put a ring terminal on the end of the new ground wire and attach it someplace that is a good ground to supply electrons from the negative side..

[Harry]

Good information. Thank you.