You're totally right about the seat heaters. The only hard part would be retrofitting the Volvo ones simply because of cost of parts. When you add up switches, wires, relays, and heating elements, the cost would probably be far more than you'd want to spend. It might be worth checking on, though, especially if you're buying with a discount.

But then check out the local custom upholstery or auto top place. Most of them do seat heaters. They aren't the Volvo kind, but I'm sure if you provided the Volvo switches for them, they would at least look original. The aftermarket ones generally work really well and the cost savings is significant. Basically you won't see much difference from the original product.
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1992 940 wagon, very low miles
as well as others.