On an original 71-72 Grabber sportlamp: On each light - there is a ground wire separate from the 2 lamp wires - check to make sure that is wired correctly. Important to remember the sportlamps light up both the tail and brake filaments in an 1157 bulb, which is why there are 2 feed wires and a separate ground. Other possible causes are bad fuse, bad switch, bad relay (inside drivers side kick panel) or a cut wire someplace in the harness. Hope this helps ..............
Just to clarify, you have a real Grabber, yes? If you have a clone no telling how it is wired. But if you have a real 71-72 Grabber, it will have this switch mounted to the bottom of the dash over near the radio.
Grabber switch in this picture: As Eric (Acornridgeman) stated, this switch it only on REAL 1971-1972 Grabbers or 1972 LDO Mavericks. I wonder of the 1972 LDO Comets had Sport lights?