Get some 1500 grit or 2000 grit wet sandpaper and wet sand the display it will bring it back to new again, then a little was when you are finished. Remember to only sand the clear display NOT the rest of it. I have done this on quit a few of them and it looks like new again.
I took the voltmeter apart, and the actual LCD display is realy dim, the voltmeter case is in good shape. I sent an E-Mail to NIPPON SEIKI asking the if there is a replacement display available but they have not replied.
forgot to mention I realy like the LTD but was not able to find a decent one here in Alberta, so I bought an 84 Aspencade and am retrofiting the factory cruise and wanted to replace the clock with a more usefull Voltmeter.