67 c30

[Longhorn Man]

clearance/marker/ID lights. That should be the ones on top of the cab. It also sounds like they have been messed with.
The federal DOT name for the lights on top of the cab roof are ID lights, being the 3 in the center, and marker lights that are located away from the center 3 and towards the edge of the roof or panel they are on. The 3 in the center are for oncoming traffic to recognise it is a truck over 7 feet wide (I may be off on the width), and the 2 outer lights are to help the oncoming traffic locate where it is in the road.