Odd electrical problem

[crafty]

Hi all, I am new to this site so please be patient if I screw up a little. ;)
Here goes, I have a 2000 Ram 3500 passenger van.
If I turn either the front or rear blower to max speed, I see a voltage drop to 12.5 volts (battery voltage). On any other setting all remains normal.
Both the battery and alternator are new, and there are no other charging issues.
I can't figure what common factor there is between the two fan units but I figure there has to be one.
Thanks in advance for your help,
Chris.

[B-300]

I assume this with the engine idling. The voltage should increase as the engine revs go up to around 14 volts. Does the same thing happen if the headlights are on? If so the alternator is probably defective. (There are 3 phases in it, if only 2 work you get only 2/3 of normal output.)
--B-300--

[Dodgevanman]

I would think there would be an initial drop, but then a recovery back up to 14V as B-300 mentions.

The 98-03 vans have a common problem of the connector to the blower motor resistor burning. There's a TSB, but not sure of the number. The blower motor resistor is located on the HVAC housing under the hood. If this is the case, this could explain the problem, BUT the rear blower doesn't run off the front circuit...I don't think.