Headlight acten up?? WIERD!!

Hey guys i got an 89 gmc sierra 1/2tn. 2wd. 350 pickup. It's got the tbi setup on it. My problem is, my fucken headlight on the passenger side like glows sometimes and dosen't shine as it should. I tried to run a jump wire from the parking light and it still did it. WHAT THE HELL? It's just the passenger side headlight too. The drivers side is fine. It's really pissen me off anybody know whats up? It's not the bulb either i put the bulb in and it is new. Anybody know whats up here? Or does anybody know where i can find a wiring diagram i just rewire the whole light system. But this thing is pissen me off! Help please guys thanks.

anybody at least got a wiring diagram?

The 99 and up mustangs are bad about it to. It is the plug that plugs into the headlight. If they are aftermarket bulbs or had aftermarket bulbs the plug gets hot and messes up. I know for the mustang you can buy a new plug, cut the old one off and splice in the new one. I did it on the mustang and used the same bulb and it worked fine. Put stock bulbs back in it and we never had the problem again.