I’m redoing my gauge cluster on my 69 fury and replaced the ammeter with a voltmeter. You will need either a Sunpro CP7985 or the clone a Bosch FST7985. Same Bosch here too. Sunpro is cheaper. I got the Bosch. Both of these have a needle that drops from the top. That is important to make the holes and depths line up.
Remove the thin metal trim ring from the voltmeter (I used plyers and just grabbed and twisted. You won’t need the anything but the guts so it’s not a problem if stuff breaks. Once its apart drop it in the rectangle hole that the ammeter was in. You will see that its almost fits perfectly. The face is the same depth as the other 2 gauges but the mounting studs didn’t sit firmly enough on the metal to make me feel confident it would not shift and have the studs touch the metal surrounds. The studs themselves are the positive and negative and they cannot make contact with the metal housing. Just like the original ammeter with its square cardboards washers. No washers I had were the right inside and outside diameter but I did find an M8 electrical ring terminal was perfect. They do NOT touch the studs just the plastic stud support. I glued them on and then for safety sake I shrink wrapped part of the studs. I added a little electrical tape around the square whole and every lined up nicely. On the back of the speedo cluster I used a piece of plastic as the non-conductive “washer” simulating the OEM cardboard washer.
Remove the thin metal trim ring from the voltmeter (I used plyers and just grabbed and twisted. You won’t need the anything but the guts so it’s not a problem if stuff breaks. Once its apart drop it in the rectangle hole that the ammeter was in. You will see that its almost fits perfectly. The face is the same depth as the other 2 gauges but the mounting studs didn’t sit firmly enough on the metal to make me feel confident it would not shift and have the studs touch the metal surrounds. The studs themselves are the positive and negative and they cannot make contact with the metal housing. Just like the original ammeter with its square cardboards washers. No washers I had were the right inside and outside diameter but I did find an M8 electrical ring terminal was perfect. They do NOT touch the studs just the plastic stud support. I glued them on and then for safety sake I shrink wrapped part of the studs. I added a little electrical tape around the square whole and every lined up nicely. On the back of the speedo cluster I used a piece of plastic as the non-conductive “washer” simulating the OEM cardboard washer.