I noticed that the temperature of the air coming out of the vents of my 81 380sl decreases when I'm idling. So I checked to see whether my auxiliary water pump was operating at idle, and it wasn't, evidently because there wasn't any voltage at its two-prong connector.

However, the blower motor and everything else on the car is working fine. So I'm now wondering under what conditions the aux water pump should be operating, and how it gets its voltage.

Thanks in advance for any help anyone can give me on this.