This "lovely" device, added to later Panteras, is as Jack describes. Appraently, a switch in the driver's seat senses your presence, sends a signal to a box under the dash.
I guess to keep the car from being started without sitting in the seat. I discussed is with Mike Drew at this weeks club meeting, and neither of us have actually seen this system function correctly.
I believe if "things somehow fail", you get out, press the inter-lock button, sit, and attempt to restart.
(While the train bears down on you !)
Chuck