How old is the battery? I would check the battery first before I started condemning any other systems. It is possible that it has enough of a charge to make the lights come on a little but not enough to turn the starter motor. The starter requires a much larger amount of electricity than the lights.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record