Instrument Voltage Regulator, aka dash limiter. Along with the ammeter, it can be a source of trouble. While you've got your instrument panel apart consider upgrading to an electronic version. A member is making and selling them on this forum.
Also available at: MOPAR Products
Here's some info from RT Engineering's webpage:
On the back of most mopar dashes (with some notable exceptions) there is a 1" X 2" metal can, with 3 terminals. This device is known as a limiter. Its function is to regulate the voltage that is being applied to the fuel/oil/temperature gauges.
Some mopar dashes don't have a visible limiter device. Instead they have the limiter built into the fuel gauge. These special dashes can be identified by looking at the fuel gauge, and if it has 3 terminals then it has the limiter built in. A-Body Rallye dashes and 66/67 Chargers are two examples of dashes that have the limiter built into the fuel gauge.
