If you mean the blower motor it's not completely straightforward. The positive feed is switched on the series, on the defender the negative is switched.
You either need to swap it round, or if you're lazy like me swap the motor connections over - otherwise it blows the hot air out of the side of the car - nice for keeping your arse warm when you get out for a fag but useless otherwise.
If you're not sure what I mean let me know
D