on ground or no power,check fuses.
Check the ground wire. You have a bad connection somewhere.
my headlights work but my taillights and dash light dont work whats wrong
The most common problem is a bad fuse.
The first check would be the fuse for the dash lights. If the dash lights are out too then it is likely to be the fuse.
Believe it or not, I have had to disconnect the cig lighter in order for the tail lights to work. Sounds far fetched but it does work!
94 mercury grand marque dashboard, hazard, and tail lights do not work?
check your ground wire in the back
Are you saying your tail lights themselves do not work and only the brake lights work. If that is the case, check the fuse, and then check the tail light bulbs.
The tail lights and the stop lights work off of different circuits. The stop lights work when the brake pedal is depressed while the tail lights work when the light switch is turned on. Look for a burnt fuse or a bad connection.
Brakelite switch is probably stuck
Check all the related fuses both in cab and under hood.
I suspect either a faulty ground circuit, or a much easier fix, faulty bulb/bulbs. You might be surprised the havoc a grounded out bulb will cause an electrical system.