To do what noss suggested (test the 5v output) do this:
1) Put the multimeter into dc voltage mode (yes you were right)
2) Touch the black (negative) probe to the ground wire on the afm
3) Touch the red (positive) probe to the +5v output of the afm
the reading should be 1-1.2v at idle (engine running of course)
also I'm not sure what you meant by "not getting any reading from the ground on the loom". How were you testing the ground?
To see if the ground is good:
1) leave the multimeter in dc voltage
2) place the positive probe on the positive battery pole
3) place the negative probe on the afm ground wire
it should read 12-14v (depending if the engine is running or not) - I'm fairly sure there is another "proper" way to test the ground but this will work fine