There is only 1 Ground shared by all the bulbs, but there are 2 power connections on 2 separate connectors, so bulbs are 1/2 and 1/2 with those connectors.
Connectors are on the back of the dash.
Bulbs are at the bottom of diagram, they use Light Blue/red stripe wires on connectors
Check voltage on both, and while it is a long shot bulbs DO burn out, and there could have been a voltage surge on the one wire that took out all the bulbs on that leg.
If Dimmer wasn't working then that could have been from an issue that took out just those bulbs.