Start with checking the bulbs.
my headlights work but my taillights and dash light dont work whats wrong
because u need blinker fluid
one of two things, BAD EARTH, or Relay switch.
check the fudes check headlights for power then check light switch
Check the daytime running light module
check the fuse on the fuse box, the bulbs,or the connections.
check the fuses - there is no fuse for the headlights.
There is a good possibility that GM trucks of that vintage had problems with the headlight switch. Check it before you replace it. Remove the 4 screws at the corners of the dasboard assembly, pull the assembly toward you and you should be able to get to the switch.
iT CAN BE WIRING OR BAD HEADLIGHT SWITCH.
if the headlights work it is bad wiring if they dont its a fuse
bad bulbs
blowen fuse or lights check fuse first