[olopezm]

Would you describe it more like dimming while driving?

If so there is a big chance a connector is dirty. It is located between the battery and the Fuse junction box under the hood; it's gray colored and has two wires on it can't remember the exact colors but I remember seeing green and yellow.

A quick test would be to turn you headlights on while idling and wiggling that connector if the lights change then you can either clean the terminals in both sides of it or cut it and solder the wires together. BE SURE TO DISCONNECT the battery, you don't want to cause a short in the wiring.

Oscar.