I understand your reasoning frank, I must add that I changed the idle control today but it didn't make a blind bit of difference to the idle. It does seem that it's doing its job by increasing the revs when the sidelights and headlights are on, it seem to take a few seconds for the idle to increase and the idle settles back down when they are turned off.
What has me confused is the idle is perfect when the alternator is unplugged.