I tested the afm on a 944 by removing it and ghetto rigging up a 12 volt battery and a volt meter to the inputs and outputs. get these things to stay and open the meter, voltage should rise as you open the meter door. I am sure you can also check resistance while it is on the vehicle. your looking for a smooth rise in voltage and a smooth drop as the door closes. if the meter seems confused, it prob needs replacement.
http://frwilk.com/944dme/afm.htm
keep in mind this is for another vehicle. but a afm is a afm. this will show you how to check one.