Morning all.
I’ve noticed something recently I’ve never noticed before. My heater works well and delivers plenty of heat. But, when I switch it on I notice there’s a distinct drop in volts shown on the dash volt gauge. Without the heater on the needle in the gauge is almost at the red line. Turn the heater on and it drops to just above the halfway mark. Is this normal or does it suggest there’s something wrong with the heater motor or battery? Alternator is a higher output one than usual and Alan belts have been changed within last month when water pump renewed.

Yes the fan draws a fair bit of current .... with the engine running and the alternator spinning, the voltage should rise to above 13.5V and there should be no change.

Have a check that the fan spins freely by hand f you can, other choice is to listen to it close by as some one else switches it off. You should hear it run down for a few seconds. Suddenly going quite could be a sign of tight/dry bearings giving more load.

Combo of drawing amps and old connectors quite possibly. With heater & lights all on, my volts on the gauge would drop below the line (and my little LED one would show <12), but the actual battery voltage was still 13.5 ish. Have replaced a couple of earth wires and is quite a bit better now.