I have seen dozens of the same problem repeated within the last year or so. There are a few weak spots in the system, the first being the copper flex board.
The circuit traces oxidize (sort of like an old penny) and add resistance to the circuit. You need to take all the lamps out from the back and use a pencil eraser to shine the copper traces up.
The other is the bulb socket itself; the brass terminals lose the spring tension and don't make good contact with the bulb. Generally, you can re-adjust the spring tension, clean the contact area with an eraser and you're good to go. The bulbs, however, tend to corrode at the contact wire. You can only replace the light bulbs to fix that.
The fuse that feeds the VOLTS lamp could be open which would cause the lack of charging. Check the fuse.
The sub-plane connector (the one that mates the flex board) could have popped out of position, causing a poor or non-existent connection. Again, oxidized copper is sometimes a culprit. If the dash is removed and not seated properly, you'll lose the connections between the "bow" terminals and the flex board.
Use the field-fix harness regardless. It will positively assure you of charging even though the connections thru the dash to the alternator may be a problem. But, be sure the "sol" fuse is not open, otherwise the field fix won't work.
Such a simple circuit, but it causes major headaches when it fails.
Look at:
http://www.installationinstructions.com/FYI/digitaldash.pdf
for some info.
