[jimh]

I think the external give away is that it has the rectangular connector, but a brown plastic body to the switch.
All the other ones I've seen pictured are either round connector with brown body, or rectangular connector with black body.

Google image search suggests that the internals of my switch is the earlier design, but mine has the later style connector, so maybe there was a transition period before they moved to the new switch design which doesn't correspond with the connector change.
I don't know why they changed the design, the newer style internals look like they'd be less reliable, but maybe the wiping back & forth makes it self cleaning, whereas mine will eventually end up with dirty/burnt contacts.
Maybe it's just cheaper to produce, but cheaper enough to be worth the cost of a re-design that late in the history of the car??

The fact they changed the type of plastic suggests it may have been they ran out of stock from the original supplier and had to re-source, maybe it got redesigned then...