My 2000 SeaRay with 3.0 Mercruiser got increasingly gimpy on the starting last summer, with the click - click of the selenoid. Over the winter we found it is an integrated starter selenoid so bought and changed the entire starter. Just went to fire it up the first time - and guess what - click - click - click with the brand new unit. We tested all wiring we could think of, its got plenty of juice, no bad breakers or fuses, don't think we crossed any wires, and when we cross jump the starter selenoid poles the engine turns just fine and will start. I dread to think after all that (its a pain to change underneath w/2" bottom clearance) we got a bad part from the shop here. But its happened to all of us before, I guess. Before I reorder and rip it out I want to be sure. ALSO, I do believe we are dumb enough to get into trouble over something simple, obvious and stupid. The Clymer Manual is no help. Now, the interesting bit - the click is coming from the part we have now identified as the "slave" selenoid. Nothing is jumping through to the main starter from that other than what comes from the hot battery cable. Should there be? Clymer implies so - though we can't figure out why --and other posts here say the slave only relates to the alternator and has nothing to do with this. At wits end - - - any ideas? Help! 
