Had a '74 Karmann Ghia that did the same thing.

The VW trick was to look under the seat for a 2-pin connector and unplug it. That way the seat always thought it was unoccupied, and therefore didn't care if the seatbelt was buckled or not... car would start regardless of seat occupancy or seatbelt position.

I would disable these switches because they were really pointless anyway. It's illegal to drive without a seatbelt now anyway, so it's not like you are allowing an illegal activity by disabling it (maybe you are, but you'll get it started then get a seatbelt ticket down the street

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