I replaced both headlights and the headlight switch. Everything works except the drivers side headlight is about half the power of passenger side light and doesn't seem to change with dimmer switch. What up? I need the headlights to work as designed. What is wrong? This is a 1991 Dodge w250 full size single cab truck.

 

1st thing I would do is check all the grounds.
By check them I don't mean just look at them, but clean up the contact points and make sure the wires are not corroded badly.

 

What grounds specifically? and where are they located exactly?

 

Try running a redundant ground from the driver's side headlight and see what happens......Ben

 

I know there is a ground on the top of the radiator support driver side. 2 wires there.

 

I checked the plug in on the headlight and found one of the 3 prongs pushed to the side and not connected. I bent it back in place and plugged it in and Voila lights working perfectly. Thanks to all who offered solutions to this problem.

 

What aggravates me about these old style bulbs is they lose their seal where the terminals go in. I tried RTV. It peels and leaks. I am going to try the Permatex that is resistant to gasoline. I call it black berry juice, forget the real name.

 

Or you could just put wiggling the connectors on your checklist with oil changes and other PM.

 

They just leak water into the bulb, then they die.

 

I bought a pair of Hella lights with replaceable bulbs. They came with a rubber gasket thinghy that fits over the back of the assembly and seals the reflector of the light with the pins of the bulb. There is a hole in the reflector to allow moisture to escape. I have had very little trouble with them other than one of the pins in the plug got loose and required wiggling.