what would cause the alternator on my 68 to squeak only when the lights or fog lamps are on?

Its the wierdest thing, lights off no squeak. lights on sqeaky squeaky.

its a brand new one btw and there is about 1 inch or so of slack in the middle of the belt.
i cant get it any tighter than that.

 

Under load when you have the lights on and its having to work harder,it takes moreto turn it.
if the belt is loose, then this is when it will slip. Tighten the belt or you may want to use some belt dressing butthats a temp fix only.

 

^x2!

 

^x4! :-)
I'm with 67 evileleanor on this one. Belt not tight enough.
The belt should be very tight.
a common way to check is:
switch engine off, make sure it stays off !
have a look where the belt is running. Where you have the biggest distance between pulleys on the belt, grab the belt with thumb and indexfinger.
You should just about manager to turn the belt over it's own axis for about a quarter turn. no more.
I hope the description makes any sense ... one of those things that's shown in 2 secs and explained in words for 15 days ....

 

that has to be it
i can turned almost all the way over.
i see the slip marks on the bracket where the bolt moved.

good call

 

uhh that's loose alright :-) let us know if it's fixed