Hi Ed,
On the new Sigmas it's not a reed switch, it's a (very expensive) semiconductor magnetic sensor, it probably does matter which way round you connect it...
On my car it's wired as follows:
Chassis side ------- Sensor side
Green -------------- Brown
Yellow & Black --- Black
Black --------------- Blue
I've taken a picture and added it my build diary for your reference, of course you have to assume that your wires are the same colours!
My speed sensor connection
Hope this helps,
Rob
__________________________
See my Build Cam to check on my Roadsport Sigma. Updated photos!
Edit to get the table to line up better.
Edited by - BadBob on 31 Aug 2008 19:20:18