When I turnthe heater on I can see the volts drop on the gauge from 14 to right aroun what I think is 10 volts.It varries from the speed detting of the fan is this normal or is there a problem.

 

That sounds like you have a alternator starting to die.. I'd replace that..

 

I have this same problem at night when I run the headlights, heater and rear defroster. I know that's a big load. Should I see a drop in the voltage while running all this. I imagine there would be some drop, but how much?

 

Dont rely on the dash meter put a volt meter on the battery and see what it does, When running the batt voltage should be around 13.8V (14).
If it is dropping much below 12.5 or so there may be a problem, Maybe the charging system can not keep up with the demand etc...More likely is just some dirty connections !

 

X2 on the weak Alt.