350 Horizon Randomly Shuts Down

[duped]

2000 Mercruiser 5.7 MPI Horizon straight inboard S/N 0L394845

Each engine has its own battery and battery switch. Starboard engine starts and runs fine. Port engine does too, but randomly shuts off completely, usually within a few minutes of starting it. No buzzers, no warning. When this happens, the light on the ignition switch goes out, and I have checked with a meter that there is no power coming into it's ignition breaker on dash when it shuts down (connections are secure).

Voltage leaving battery switch is solid 13.7, and connections at battery are secure and clean.

I tried resetting the main 50 amp breaker on engine but it did not seem to be tripped, and pushing the red button did nothing to bring it back. The strange thing is that after sitting for anywhere from a few seconds to ten minutes, the ignition switch light comes back on and the engine can be restarted. On our last trip out, it did this for a bit and then ran fine on the 30 minute haul home. I got out there yesterday, and it was shutting down again.

Any chance that the engine breaker could still be faulty? Looking at the manual, I'm not sure there are any other things that would cause a loss of power at the ignition breaker. I would appreciate all advice.

Thanks!

 

[alldodge]

Does the boat have a central key switch below deck or two key switches at the helm?

 

[duped]

The ignition switches are just Carling rocker switches. Down is off, middle is on, up is start. The battery switches are keyed and when they are on, everything is live. There is no other switches or breakers on any of the other panels. According to the factory wiring diagram the 50 amp engine breaker should be directly feeding the ignition breaker.

 

[alldodge]

OK, then the rocker switches are just like key switches. When the light goes out you have checked the switch and the 20 amp ignition breaker and there is no power (12V) when it happens. The wire feeding the 20 amp and switch is Red/Purple and comes direct from the engine harness connector. Start first with removing the main engine harness connector and check the pins for corrosion or loose pins.

The Red /Purple comes from the 50 amp breaker on the motor. So need to measure voltage on each side of the breaker

 

[duped]

Thanks for the advice and info, I will check these things out tomorrow.

 

[Bt Doctur]

check the main engine harness plug. The clamp is supposed to be snug, not tight

 

[Chigwalla]

While the problem is occurring, do you have battery voltage at the breaker's output terminal ?

 

[duped]

Checked a few more things today. Seems like the issue is getting worse. I flipped the ignition on, and it didn't even get through the two beeps before shutting off, and it hasn't come back yet.

I have verified that when it is doing this, there is voltage coming in and going out of the 50 amp engine breaker. I disconnected the round main engine connector, everything looked clean and undamaged. Found a pinout and verified that 13.7 volts is at least making it to the purple and red wire on the engine connector. I assume something must be screwed up further down the line, between the engine and the breaker at the helm.

Assuming I can't find where the circuit is broken, is there any reason that the engine harness HAS to provide power to the ignition breaker, or could I just tap into the main buss bar at the helm?

 

[alldodge]

I would go to the helm switch and see if there is power on the Red/Purple. I'm starting to think you just have a bad switch. You don't want to power from the buss bad, it needs to come from the motor connection.

 

[duped]

No Title

According to this cheesy wiring plan they gave me, the voltage goes through the breaker and to the ignition switch. Or am I looking at something wrong? I have no voltage at the breaker. I haven't probed the switch, because I assumed it's fed by the breaker?

 

[alldodge]

That is only a representation not an actual diagram. Power comes in thru the Red/Purple through a 20 amp fuse to the common on the switch. When turned to ON, power goes thru the neutral safety switch and then to the gauges. The neutral safety switch is in the throttle handle or may be on the shift plate. The power goes thru neutral safety then to the motor



Actual wiring, and no issue with bypassing the neutral safety switch, note the Yell/Red wire for start, and the purple for run. Just replace the key switch below with the rocker switch

 

[duped]

Okay, think I'm starting to get it. My neutral safety switch is on the top of the trans, but I ruled that out because on the starboard engine I can still switch the ignition on with the trans in gear, just not start it. I will dig a little deeper in the connections at the helm tomorrow.

 

[alldodge]

The neutral safety switch only controls the start circuit. If your not in neutral you cannot start the motor, but your gauges should come alive and so should the fuel pump. With your light not coming ON and the motor dying, this is the ignition power circuit, (purple wire) not the start circuit

 

[duped]

So far today I've swapped the ignition switches between one another and replaced the port engine ignition breaker with a new one I had lying around. The starboard engine starts fine using the switch out of the port's spot but I still get nothing out of the port motor. Also, doing some more probing with a meter, the big red wire going to the port ignition switch does have 13.7v, but no matter what I do or which switch was installed, I cannot get voltage out of the purple wires. I thought this would mean it's the ignition, switch but must be something else because both switches seem to work fine on the other engine.

 

[duped]

So to recap, I have voltage at the 50 amp breaker, I have voltage at the engine connector. I must have made a mistake when I checked the ignition breaker before because I do have voltage there, and voltage to the red wire at the ignition switch. But that is all.

 

[duped]

Tried some more things. When I jump the big red wire to the yellow / red striped wire and the starboard side, the engine cranks over. When I do this on the port side, nothing happens. When I go down to the solenoid and jump it, it does crank. Not sure what this means and doesn't seem to explain the lack of any ignition power...

 

[alldodge]

the big red wire going to the port ignition switch does have 13.7v, but no matter what I do or which switch was installed, I cannot get voltage out of the purple wires

The purple wire supplies power to the ignition circuit. So jump from the Red going to the switch to the purple and things should come on, if it does not, then its either the switch (which works fine on the other motor) or the connector terminal which is connected to the Red or Purple wire is bad/corroded under the insulation.

Either that or there is a fuse in the purple wire, which would be unusual

 

[duped]

I replaced the spade connector on the red wire because I accidentally ripped it off when I was playing musical switches. Jumping the red to purple does nothing. No gauges, no fuel pump, nadda. I found a new switch at the marine store, put that in and still nothing.

I have continuity between the purple wires running from the ign switch to the gauges. The purple wire runs down a tube with the rest of the engine harness and through a bulkhead. It is all wrapped up with wire loom and as far as I can see, it's undamaged and no fuses that I can see.

 

[alldodge]

Jumping the red to purple does nothing.

This is your issue, right there. your Red (should actually be Red/Purple) should have 12V all the time and it comes from the 50 amp breaker on the motor, thru the engine connector, to a 20 amp breaker or fuse to the switch. So if your not getting 12V on the Red wire, then its either the fuse, wire or one of the connectors.

 

[duped]

No Title

Thanks. The confusing problem is that I DO have voltage at the big red wire on the ignition switch. I have checked multiple times as I could not believe it myself. Jumping that red wire to the purple wiring next to it on the switch still does not do anything. The switch has three terminals worth of purple wiring daisy-chained together, and I have checked that it all has continuity with one another and the gauges. The ground to the switch and gauges also checked good.

The only thing I'm thinking is the connection on the breaker or the ground is only good enough to pass voltage to my meter but somehow fails under load. I'm going to re-terminate everything down there tomorrow and hope for the best.