Interior Lights Dim When Braking

Hey everyone, I didn't know if this a place to post this but I kinda need an answer asap. My dad was coming home today and when he was pulling in the driveway everytime he braked the lights inside the truck (he has an 1997 ford expedition) would dim alot. The last time they dimmed like this his alternator had to be replaced (this was done just a few months ago) but they didn't do it when he braked. He still has to go back out to work tonight so if someone could respond with a possible reason why it would do this that would be great. Thanks in advance.
-Mike

Mike -

Do his lights dim when pressing the brake pedal down when the vehicle is not moving, or do they dim when he his braking to come to a stop? If they dim when he is coming to a stop, he may have gotten a bad alternator or his battery life may have been diminished from his old alternator. Have his alternator checked and then his battery voltage.

Jason

It dims anytime you press the brake when the truck is on- whether it is moving or not. I tried it after it was off last night and nothing dims at all.
I did some more searching last night and found this page- http://www.uk-hotrods.co.uk/Technical/Electrics/trouble_shooting_electrics.htm
At the bottom it talks about poor earthing. It mentions about the radio starting up by itself, and his truck does that once and awhile (he said it happened last night). Does anyone know if poor earthing could be the whole problem?