Brake lights

1 have a 2004 Sr5 Tacoma. My brake lights work fine until I turn my headlights and tail lights on. When turned on the brake lights illuminate, but the 3rd brake light works as it should. Any suggestions

 

If you purchased it used, see if someone's got aftermarket wiring connecting fuses or relays. I bought a vehicle that had a similar issue, and it was because the previous owner had taken out some aftermarket lighting but done a crap job removing the wires/add-a-fuse/etc

Your brake lights are getting a constant +12v from the headlight/switch, one way or another.

 

Got it figured out. The loose part of the brake light/ tail light socket with the 2 contacts was cockeyed on both lights. Repositioned them the correct way and we're good to go. Thanks for the advice much appreciated