What would cause the battery gauge to bounce when using the turn signals on a 87 celebrity sedan?

In many cases, battery charging gauge fluctuations are a symptom of the charging system not keeping up with the additional electrical demand of a blinking light or wipers or other intermittent electrical drains. I would first have the battery checked to see if it is holding charge. If the battery checks out OK, the likellihood is your alternator is failing. More than probably it is your alternator. Ya probably one of the six diodes in the bridge are open, Or the brushes to slip-ring connections are jumping (dress slip-rings and replace brushes. GETERDONE!