Ok so I recently started having issues with the highbeams in my 83 k20, the highbeams will work perfectly fine for about 5-10 minutes then they start flickering between low and high. I was actually driving on a trip from salt lake Utah to Phoenix Arizona and it had gotten dark on the interstate and of course that's when it started to happen. Very dangerous situation so I need to get this fixed asap. Is this caused by the dimmer switch on the floor going bad? Possibly old wiring? Any help is appreciated, I sure hope I don't have to retire the headlight system.