You should look for a water leak above the amp gauge location. Wiper pivot or windshield gasket. It can damage your headlight switch also. I shipped the only used gauge I had to a 73 owner here a couple weeks ago.
Beware of sellers offering this amp gauge.
1976 valiant duster amp gauge | eBay
The 76 model gauge looks nearly identical to yours from the front but it is a totally different one year only animal, and will not work.
Yep your read between the lines that ma mopar finally did change this gauge because a water leak would shut down the whole car. Sellers dont know the difference and offer a gauge listed for "72 through 76 model".