i dont have a mutltifuntion switch as mine is a 72,but i kow what bad grounds can do to a entire electrical system is not wired properly.i was a gen mechanic in the army and seen what bad wiring that operators can do.starts fires, burn out entire circuits in whatever they are hooking to,or just generally not running properly.same thing applys to vehicles.i had to rewire half of my truck when i got it because of the half assed wiring the p.o. did.grounds are easy to replace.a couple extra ones added and tightness of the ones you have goes a long way to make everything electrical run properly.as for where i hooked my extras up.i put a new ground strap from the engine to the firewall.then added a new ground into the wiring from the dash guage harness to the firewall.then my guages worked much better and also added a better ground for to lighten up my dash lights better.sounds like either bad bulbs,multifunction switch,or a bad ground.2 of them are cheap to check.the multifunction swicth being the only expensive piece.and a lot harder to get to.make sure to check all your wiring connections are clean and not rusted or corroded also.just having dirty battery terminals will cause a loss in power.