blinking "ign" light

[Walt Philipson <WaltP@Anspach.com>]

I've noticed this twice recently on the same stretch of road. This only
occurs at night with my lights on. After driving through town I get on an
open stretch of road. As I accelerate, my ign lamp will momentarily light
up, then fade. Occasionally it will blink while I'm holding a steady 60 mph.
The only thing I could think of is that the belt is slipping, but it seems
OK. The alternator is the stock unit but was rebuilt about 18 months ago. 

Any ideas?

Walt Philipson
74 TR6