My voltmeter on our 420 started reading less and less then 120v over a period of time and now is reading 0 volts. There is definitely 120 v measured at outlets and at the back of the voltmeter. I am struggling to get one that fits the opening. Blue Sea is a little narrow and a bit too tall and is 1/8" too tall to fit in the back. I can modify the opening but would like to see what others have done in this case.