1991 Accord. My left headlight is exactly as dim as the driving lights, and when the brights are on, it shuts off. The right headlight is fine. Is it the bulb or the wiring. THanks

 

check your wiring, it sounds like a bad/weak ground

 

the high beams are on their own separate ground, i'd suspect a bad high beam bulb there. replace the bulb. if it works fine you know the power is fine for the low beam bulb.

the lows also share the same ground, so if only the left has a problem i'd suspect a bad bulb or a problem in it's ground wire itself(bad bulb socket?). if a new bulb and ground wire don't fix it,it could also be a problem with the voltage wire between teh bulb and the split to the high beam bulb.