alternator gauge drops and reads low when driving

FOURTEEN POINT NIIIIIIIIEEEEEENNNN??????!??!??!!??!?!?!?!


That is way too HIGH.

Your running voltage, engine warm, should be optimal 13.8--14.2, not below 13.5, nor above 14.5

Start with this:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

You may have one, or a combination of several problems

1.....may have an older "roundback" alternator with limited output, IE 35 A or so

2....The above may not be in good shape, with worn brushes, one bad diode, etc

3....There's always the belt, as in..........slipping

4.....Voltage drop in either the ground, the ignition harness or both, causes OVER voltage. Hundreds of threads on here about that

5....As in the posted MAD article, problems at the bulkhead connector, the ammeter, and ignition switch connector and switch can cause and add to these problems.