bad starter wire?

I have a 99 355 with a starting problem. The battery was check and fully charged, the starter and solenoid was check and are good. When I turn the ignition key and am getting 12volts to the starter but it won't crank. I can start the car by giving the starter 12 volts from an independent source. the problem seems to lay somewhere between the the ignition (steering colum) and the starter. Is there a fuse or relay for the starter? I heard of a seat sensor that could prevent starting the car. Is this true of the 355?

 

it was a loose fuse. Also noticed that my 15 amp airpump fuse was blown. switch it to a 20 amp and hope that solves my CEL.