1990 GMC Truck Taillights

The taillights on this vehicle will not come on when the headlights are turned on.
-Brake lights work
-turn signals work
-reverse lights work
-hazards work

All lights are bright
The vehicle has an alarm on it- when activated/ deactivated- all taillight bulbs flash as they should

all bulbs work, fuses seem fine, cleaned and reconnected ground

at the same time this problem started- the interior dash lights went out- dont know if its relevant

turn signal switch, nuetral safety switch replaced about a year ago
help please- thanks