If a bunch of lights on one circuit are out (but not others, like the tails or other side clearance lights,) you might have a bad ground in that group of light assemblies. But they're all run to one ground location...
2015 XLR Hyperlite 30HFS5 (mods being performed regularly)
2009 Salem LA 292fkds (gone)
Nights- ('12)23 ('13)23 ('14)15 ('15)31 ('16)25
2014 Harley Davidson FLHX (XLR cargo)
2014 VW Jetta TDI (diesel sipper, camping support vehicle)
2011 Ram 2500 CC 4X4 CTD, B&W Companion (toy hauler hauler)