The only device similar to this that I have seen in a 914 is the 1974 "Infamous Seat Belt Interlock". This device would break the connection between the ignition switch and the starter motor, unless the driver's seatbelt was fastened
and, if it detected someone in the passenger's seat, the passenger's belt had to be fastened as well.
This system usually makes itself known as intermittent starting problems because the relay or wires got wet and corroded.
You can fit a simple switch in there if you like. Not as cool and high-tech as a printed circuit board, but just as effective.
--DD
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Pelican Parts 914 Tech Support
A few pics of my car:
http://www.pelicanparts.com/gallery/Dave_Darling