I just answered a question similar to this, here's what I posted.
1999 Other Saturn Models 4 cyl Two Wheel Drive Automatic 199985 miles
we have a 99 saturn sl1 when we picked it up I found it funny that when I hit the brake peddle that the dash lights all come on. Just as if you turned your lights on. After further looking into the problem we find that we have no brake lights when we have the headlights on but they do work just fine when the head lights are off. Also the headlights dim when we hit the brakes when the head lights are on. What and were can I start to look for a problem or is this something normal.
It sounds like a bad or broken ground wire to you tail lights. Let me start by saying I drive a 18 wheeler for a living. The wires for the tail lights on them are exposed to the weather. It's common for a ground wire to rot or brake. What happens then is when You hit the brakes the brake lights try to light up but since there is no ground the light socket finds a way to complete the circuit (causing a short circuit). That would be the wire for the running lights. That's why your dash will light up when not turned on (false ground) and headlights dim when turned on (wire is in hot)
Your issue is very similar to this I would start with the ground wire for the tail lights and work my way to the ground for the fuse and braker box.
Friday, January 11th, 2008 AT 8:22 AM