[Vwdiesel] Cooling issues

[Rudy]

My 1984 Jetta runs about 20 degrees warmer when I have the lights and or
wipers on (Seattle), I've watched this and its consistent.
 
Thought maybe it was the alternator water pump belt but the power steering
belt is tight and can't slip, they both power the water pump.
 
I'm wonder if the added load on the alternator could make that much
difference in the running temp or does something sound not right?  I saw
some posts about this a little while back but can't find them now or don't
know how to find them I should say.  Anybody have any thoughts on this?  
 
Rudy