My car has 118,000 miles and I just replaced mine yesterday. My lights were doing this weird normal/dimming/normal/dimming thing while I drove...regardless of rpm or load. After 4 weeks of that...my little battery idiot light came on. Took it in...they tested it...yep...bad.
FYI...I actually have a dealer that I trust. Versendaal Lincoln/Mercury in Holland here. Called them up...$160 labor to replace it. Considering all I've read about what a PITA it is...I went for it. I also got a Motorcraft alternator..so in the future if I had any problems...I'd just go right back to them.
And another FYI...every nut/bolt they removed was rusted like mad. For a 3 hour quote...it took them 6 hours. Plus they gave me a lender to drive. So basically..they didn't get much profit off me.
