It is possible that the last time you ran it you shut the engine off in gear and then shifted the lever to Neutral? There is a neutral safety switch in the shift/throttle control that won't let it start if it thinks the gear shift is in fwd or rev. If you shut off in gear and then don't get it back in Neutral just so it can happen. Back when I didn't know how to properly adjust my Cobra shift system, every now and then it would not go into neutral unless I shut off the engine (that was many years ago, now it shifts with 2 fingers LOL). If I was not careful about not putting it properly back into neutral it would not crank. I would try that first. Then you can troubleshoot if you are getting voltage at the starter solenoid. First hook up a volt meter from the big stud that gets the hot from the battery and a ground. You should have 12 volts there as long as the batt switch is on. Then, hook up the voltmeter positive lead to the small connection on the starter solenoid (often a yellow or yellow striped wire). Hook up the neg volt meter lead to a ground. Then have some try to crank it over with the key (make sure you are not right next to the drive belt then LOL). If you get no voltage there then your problem is likely between the ig switch and the starter. It could be the switch, the neutral safety switch in the shifter/throttle control, or an assist solenoid if your model uses one. Another test you can do to bypass all that wiring to test the starter is this: go to an auto parts store and buy a remote starter switch. This is basically a pushbutton switch with 2 wire leads attached. You hook up one lead to the small terminal on the starter (Yellow or yellow striped wire) and the other to the large positive terminal on the starter that comes from the battery. When you push the button in, this puts 12V directly to the start terminal. If the engine cranks then, your problem is upstream in the other items I mentioned. The gauges all work, trim works, etc? That would rule out the fuses in the main engine harness.
Back in the old days we would short a screwdriver from the big plus terminal to the small ig terminal on the solenoid. But that is dangerous and can make sparks which you don't do on inboard boats.
We also used to make our own remote starter switches, with simple push button switch, 2 wires and alligator clips.
You need to get a Volvo or Merc wiring diagram and trace the problem back to the source. It could be something real simple but not obvious. Make sure that shifter REALLY is in NEUTRAL.
READ THIS:
http://forums.iboats.com/mercruiser-i-o ... 67035.htmlI just replaced the 16 year old original starter on my old 98 Jeep which is now my son's. We pretty much knew the starter was bad but I was relieved when I checked for voltage at the small ignition terminal and found 12 volts...that way we knew for sure it was the starter (easy to replace) not the wiring (not so easy to trace). Changing the starter on a Jeep 4.0 six is about as easy as it gets...even on a 25 degree day about a month ago...I had to keep the heater running on my other Jeep to keep warming up my fingers LOL....