If your '78 has two alternator belts like my '83 then either your belts are very worn out, or most likely loose, and they need to be tightened. Push on the belts with your fingers, and see how much deflection you are getting. (Engine off, of course) I bet it is more than 3/4 of an inch.
"...rationality of thought imposes a limit on a person's concept of his relation to the cosmos." -Nash
04/71 280SE 195k
09 Jetta TDI