I bought this eBay item to repair the failed voltage display on one of my Harbor Freight 45 watt panel kit power distribution boxes.
http://www.ebay.com/itm/390341332475$10 including shipping each from China was a lot more than some of the others offered that looked like this one, but I searched until I found a 2-wire hookup with built-in polarity protection. Most of the $1 volt displays had fair warning in the ad that they would fail quickly if you hooked them up backward. I hooked mine backwards at least twice during the repair so I can say that this one works as advertised.
The repair isn't to OEM. The original display
does not have polarity protection and has 4 wires. The main sense/power feed is not the + battery terminal in the back, it's off the board
near where the + from the battery terminal feeds the board. Polarity protection means a diode in this case, but diodes have a small forward voltage drop. When I hooked the replacement off the board like the original it read 1 volt low, as expected.
That meant I couldn't switch the replacement with the main power toggle unless I recalibrated the display, so I tapped the battery + to the push button switch and grounded the display to the - battery terminal. That way I can see the display even if the main switch if off, but I can still turn off the display with the push button.
Personally, I like it better this way. I can use the pdu as a voltage monitor without the drain of the rest of the pdu's circuits.
The replacement display is maybe 1/4 inch larger in both dimensions, so I enlarged the hole with a Dremel.
There are red led volt displays like this one,
http://www.ebay.com/itm/221048898851, but they warn openly in the ad agaist hooking it up backwards, so I settled on blue.
The blue looks washed out on camera under flash but is actually quite bright and easy to read in bright or dim light.
