Bypassing much of the wiring and running straight to the starter using jumper cables is a good suggestion. What do the battery cables look like? Are the ends in good shape, shiny and clean? If any of the cables or ends are bad, or if you have a battery selector switch that could be corroded also, the starter will not spin the engine. If you do not have the proper testing equipment to measure the resistance, or the knowledge to do it, you could try the following. Attempt to start the motor by leaving the key or start switch on for 30 seconds, or so, and then quickly put your hands on all of the cable connections, battery terminals, solenoid and starter. If you can find a very warm or hot spot that could be where you are having problems getting enough power to the starter. A low tech ohm meter so to speak.
The odds are against it, but I have had "new" starters that did not work. It might be worthwhile to pull the starter off the engine and run some power from the battery that is on your boat to it and confirm that it is functioning. Be careful, the starter can jump a lot when it first spins.
Last edited by FarCry; 05-08-2008 at 10:53 AM.