Yikes, ok do the headlights and parking lights work properly when the headlight switch is pulled on? Yes, then the service light switch is either toggled up or it is bypassed completely somewhere by the toggle switch. Leave headlights off, right toggle drive lights down then left toggle blackout on go up and let go back to center. Now all blackout lights on until you toggle left toggle down, toggle returns to center, all blackout lights off.
Now all lights off until right service light switch is toggled up and stays there. Now headlight switch works as it should like civi truck. I just went outside to look at, also under dash and you can see clearly under without much heartache to see if wiring has been molested at toggle switches. Grounding wires are very important in this wiring setup as there is no metal contact as all blackout lights are plastic. cuvrus has very good advise and use test light to verify that you have current as afterall they are plastic and 30 plus years old. Good Luck