In the Astra G, on the lowest part of the centre console, in front of the gear stick gaiter is a small plastic panel.

This panel houses your traction control button. (if car has TC)

If you remove the panel you will find 2 spare electrical sockets.

These are the sockets which would plug into the switches for the heated front seats. (if they were fitted)

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Thanks to Matg, NuttyNovas, LordNikon