Internally Regulated Alternator Kit...???

Your gauge is an ammeter, and the D and C stand for Discharging and Charging, respectively. This is a good link for you to read.

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

Lots of people, including myself, have bypassed the gauge by simply disconnecting the two wires on the posts on the back of the gauge, and bolting them together on one stud or the other so it bypasses the gauge. Then you can hook up a simple Volt gauge.

Hope this helps a little,

Kenny