something i have seen several times is a one of the high beams will burn out & the operater will not notice it. they will only notice this when the other one burns out, then you don't have any bright lights. don't know if this is your problem but have seen this happen a bunch, might check to see if you have power to the headlights on brights ,if you do, might try new bulbs. park lights will/can work even if headlights go out, they work when pulling light switch part way out. just by reading your post i don't think you have a switch problem, is possible especially if the lighs are actually on bright while on dim side, but i would think if it was shorted out the indicator would be on. I really think you need new headlights or possible wiring problem.