Ignition Fuse Pops, Weird Issue

Vegas Naturist

Petty Officer 3rd Class
Joined
Sep 15, 2011
Messages
81
I haven't been on here in a while, but I have a weird issue with my '97 Capri 1950 I need some insight on.

We took the boat out recently, and the boat ran flawlessly for the first several hours. As we were leaving a cove to head home, every time I shifted from forward (or reverse) to neutral, the ignition fuse would pop and obviously the engine would stall. I'd replace the fuse and the ignition would energize, the engine would immediately start, and the boat ran fine. It did this consistently for the rest of the outing.

I had this issue briefly last season, but it seemed different. Last season we were at Lake Havasu and I mistakenly left the nav lights on all night. The battery was already old and questionable, and was dead in the morning. I replaced the battery and the ignition was dead. I checked and replaced the blown ignition fuse and the boat started. I figured the fuse blew because low voltage, given the same load, draws more amps. At the time, all I had was a 10 amp fuse instead of the original 15 amp fuse. Every time I shifted from forward (or reverse) to neutral the fuse would blow. I figured it was because it was a 10 amp fuse. I bought some 15 amp fuses and replaced the 10 amp and did not have the problem the rest of the trip.

Now I'm trying to isolate the issue given the fuse is the proper capacity and the issue has reappeared. The only thing that happens when shifting is the cutout switch momentarily cuts ignition power to the distributor module so the engine torque "skips" to allow the shift. This switch, as I understand it, is a normally closed switch that OPENS a power circuit, so why would it blow a fuse? I checked the wiring from the fuse block (red wire) to the ignition switch and found no issue. I checked the ignition circuit (purple wire) all the way back to the cannon plug (pin 5) and found no issue. I also found no issue from the cannon plug to the cutout switch (and all the other places the purple wire goes to on the engine IE alternator exciter, electric choke, etc) and found no issue. Now I was checking the circuit with the key on, engine off, but I could not duplicate the issue, even manually triggering the cutout switch. Why was it doing it on the lake?

If the cutout switch was shorting to ground when triggered, it should have blown the fuse key on, engine off, which it didn't. If the distributor module was bad, it would seem the engine wouldn't run and it would blow the fuse as soon as it's replaced (shorted module).

What am I missing besides the "Ghost in the Machine" being angry?

John
 

Vegas Naturist

Petty Officer 3rd Class
Joined
Sep 15, 2011
Messages
81
Update... In case anybody is interested...

After digging into the issue a little deeper, I found I was under the false premise that the cutout switch is normally closed. It is normally open, and when triggered doesn't cut power to the module but sends power. According to my Fluke, there was no issue with the cutout switch, it stays open until triggered and closes as it should. There is also no short to ground in any position. This left the ignition module as the most likely culprit since the switch is operating as it should and when closed does send power to the module. And the module is the last thing in the circuit. I replaced the module and "road tested" the boat. The original issue did not reoccure.

Is it fixed? At this point I'd say most likely, however without being able to difinitively show the module was defective, time will tell.

John
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
25,912
What year MerCruiser? When you say cutout switch, do you mean shift assist switch on shift linkage?
 

Vegas Naturist

Petty Officer 3rd Class
Joined
Sep 15, 2011
Messages
81
What year MerCruiser? When you say cutout switch, do you mean shift assist switch on shift linkage?
It's a 1997 Bayliner Capri 1950, just like it says in my signature. Yes, the shift assist switch on the shift linkage.

John
 
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