My firstpost here. Have a 98 Expedition on which my starter was acting up so had it replaced. A couple of days later my battery light started coming on, the running board lights on the drivers side went out and the headlight on the drivers side goes dim. Had the alternator checked out as well as the battery and was told both are good. Any ideas?

 

Check the wires from the battery. Cut back some of the insulation and look for greenish or yellowish power forming inline. If the battery cables corrode back into those wires, you'll get sparatic issues. And they are cheap to replace.

 

If the battery light is coming on, mostly at higher RPM's, it is a sure sign your alternator needs to be replaced.