Has to be voltage drop. When I'm sitting at light with the heat on blower motor going I noticed the voltage drops greatly. When I start going and the alternator powers up again the volts go up. I tried this today while it is snowing out I turned off the heat so that the blower would stop and turned on the rear wiper and it worked fine, but will not work while blower fan is on. What could be causing a voltage drop like this? I don't remember it doing something like this before. Also notice the voltage meter on dash when sitting at light with turn light on the meter bounces with every flash. Could this be a sign that my alternator might be on way out?