If you are referring to the brake lights it is probably a bad brake light switch. Your vehicle may also have daytime running lights which would be on without the parking lights.
WHAT ARE YOU DUMB REPALCE YOUR LIGHT BULBS STUPID! Not stupid replaced circuit boards checked fuses ran test light . When headlights are on no brake light or taillights and have all new bulbs stupid. Turn headlights off brake lights work, so figure that out smart man
The obvious would be the bulbs are burnt, then look at the fuses for the taillights, and then the wiring. The holders where the lights themselves plug in are bad sometimes; you can get them cheap at a pick-a-part yard.
faulty switch
GO AND BUY I NEW light bulb !
only thing left to check is the light switch
Check the switch.
Check the light switch for a burnt connector. Your Taillights are on a different fuse than your headlights or directionals I would recheck your fuses again. Could also be worth checking for open circuit wiring and bulb holders?
its the tail light fuse
Check the fuses and the bulbs.
Bulbs? Fuses? Relay? Dimmer switch? Headlight switch?
it could be you headlite switch or a broken wire under ur car
The switch.