Hello,
I have a 2003 Ford explorer with 104k miles that we got brand new. At about 90k miles, I noticed that the lights were getting really dim so I swapped the alternator for a new one from the closest Ford dealership. Although it fixed my dimmed out lights, when the car is idling, the lights (and instrument panel) dim and brighten continuously, maybe about once every second. Don't have the problem when the RPM is above idling (ie driving). Thanks in advance.
On a vehicle that old pay particular attention to grounds, especially the ground cable between the engine and the chassis.
get your battery load tested. They often fail together.
Double check all the connections on the battery and alternator, as well as the grounds. It should all be clean and tight.
