Pontiac Repair: weak 2002 Grand Prix headlights, digital volt meter, grand prix gt

Question
I have a 2002 Grand Prix GT 3.8L non-supercharged and the headlights seem to be very weak.  And the bright lights aren't any brighter than the dims.  It's my wife's car so I don't drive it a lot, but to me it seems to have gotten progressively worse.  The alternator has been changed recently as well as the battery with no change in light output.  What might cause the headlights to be way dimmer than they should be?  No other driveability issues.  Runs fine and all other electrical components seem to work fine.  Thanks for your help.

Answer
Hey Jeff.

Well it could be a few things. A bad ground would be my first guess. if you have a digital volt meter pull out the head lamp assembly and back probe the power and grounds to the hi and low beam lights. you should have battery voltage between the ground and power feed. If not then isolate the power and ground what I mean it hook the ground lead of the meter up to a good body ground and then check the power feed If it reads battery volatge then you know you have a bad ground and vise versa for the gound but hook the power lead up to the battery, once you find a bad ground or power you have to trace it back to where the resiatnce in the ckt. is. The second guess and it's out there is this if there is any water inside the headlamp capsules that could have an affect on the lamps also the lenses have a tendency to cloud from the sun. That's obvious but worth mentioning none the less. Good luck :)