Ignition circuit fuse blowing

[rbezdon]

I am having an issue with blowing the "ignition" fuse in a 2003 Caravelle with the Mercruiser5.0MPI. I replace the fuse and the boat runs fine for an hour or two and the fuse blows again. Checked the obvious (loose or pinched connections under dash, engine comaprtment etc). The fuse blows some times at idle speed in calm water and some times cruising on the lake. I have the Merc Service manuals which show the engine and trim wiring harnesses but I am looking to find the wiring diagrams for the rest of the boat. It seems Caravelle went out of business and is just in the process of restarting operations so getting documentation is tough. Does anyone out there have a set of wiring diagrams??

 

[Don S]

Re: Ignition circuit fuse blowing

If the Merc inst panel was used on your boat, then below is the wiring diagram. You don't have any accessories running of the purple wire under the dash or on the engine do you?

 

[rbezdon]

Re: Ignition circuit fuse blowing

If the Merc inst panel was used on your boat, then below is the wiring diagram. You don't have any accessories running of the purple wire under the dash or on the engine do you?

No, the Merc panel is not used on Caravelle. There is a fuse panel located under the dash which has the fuses for the blower, Acc, Bilge, Lights etc. Unfortunately, the boat is an hour from here so I can not see the color wire feeding the fuse panel right now but from the Merc drawing it may be Red/Purple. I assume the fuse panel is connected near Object "H" in the Merc drawing as "H" referrs to note 2 in the drawing where Merc allows up to a 40 Amp connection. The fuse maked "Ignition" in the panel is the one that keeps blowing which likely connects to the B terminal of Switch "F". I also then assume that the "on" position of the ignition switch is connected to the some of the circuits in the fuse panel which are ignition controlled. It is just not clear to me where the fuse panel taps in and what else may be connected to the 15A ignition circuit.

By the way, thanks for the diagram but it is the same one I have in the Merc service manual. I need something likely Boat Manufacturer specific although I am betting most manufacturers use similar connection schemes and color codes for the wiring.

 

[rbezdon]

Re: Ignition circuit fuse blowing

Well, i spent the last 4 or 5 hours trying to track down the short blowing the ignition fuse and I am ready to sink the thing. I tried everything to isolate the problem but it is still there.. All I kn ow more than before is the Caravelle fuse panel is powered by the redpurple wire and the ignition fuse is inline with a smaller red/purple which feeds the 12V connection on the ignition switch. The ignition switch has 5 wires where as the Merc drawing has 3. the red/purple for power in, the purple which is the switched 12V for powering all of the boat and engine, the yel/red for the starter solinoid and purple white connected to purple and a red which has 12v switched on just like the purple but when the switch is turned off it drops quickly to like 6 then drifts very slowly down.

Since the purple is the main feed I assume the overload is on that line but there are literally dozens of purple connections. If I turn the ignition to on all of the purple and red are energized and the fuse does not blow. Enev leaving the ignition in the on state like this for 10 minutes or more, everything is fine. Start the engine and in about 2 to 5 minutes the fuse blows, even a 30AMP. Replace the fuse and all OK for another go of about 2 to 5 minutes. I tried running trim up down and turning the steering while running trim and mothing. Fuse blows when engine is running in meutral or in gear. I cant figure out what else kicks on when the engine is running that is not powered with the ignition "on". any ideas??

 

[Don S]

Re: Ignition circuit fuse blowing

It is possible to disconnect the main engine harness from the helm.
Just unplug the Round 10 pin harness connector. Make up a jumper wire with a 10A fuse in it. Hook it up directly to the pin with the purple wire in the engine side of the connector and see if the fuse blows.
Do you have a serial number for your engine handy? Year doesn't tell me much.

 

[rbezdon]

Re: Ignition circuit fuse blowing

I do not have the boat here so I'll get the S/N this week end. I did take a jumper and connect the Battery to the purple lead with a fuse and ammmeter. No fuse blew and current draw was about .6AMPS. Nothing I could do without the engine running would make the fuse blow. It only seems to blow with engine running. Can I start and run the engine with the main wiring harness disconnected as you suggested above?? Seems at least I would need to connect the 12v (red/purple) to the yellow/red to get the starter solinoid to engage anlong with the jumper you suggest. However, this would leave all of the other sensors and guages open.

Also, some one suggested to me I may have a bad alternator. One going "full field" or possibly a deffective diode trio. While I am a respectible shade tree mechanic and have seen my share of alternators fail, I have never seen one that can take out a fuse. Now, as you suspect, most the my shade tree experience is on cars, I know the basic operation of the electrical system is the same for boats, just different safety protections built into the fuel and electrical system. Have you ever seen an Alternator take out a helm mounted fuse before?? I am planning to completely disconnect the alternator next weekend and run the boat on the battery alone just for gins and see what happens.

 

[rbezdon]

Re: Ignition circuit fuse blowing

I did pull back the ruber protectors on the alternator connections to look for loose frayed wirse and corrosion. None seen. Both the post (orange) and the double connector seemed solid enough but who knows, after all I am having a problem. I will try next time I get up there, running with the connector and the orange wire disconnected. After all, I can not even get the boat out of the water and onto the trailer and the ramp is like 10 to 20 minute boat ride and I can't even get to the end of the channel from my house. I am an electronic engineer and a fairly adept shade tree guy but this has got me stumped so far.

One friend suggested for the heck of it to hook up to the ECU and look for any fault codes. Does this Merc MPI use the standard OBDII?? Can I use my auto OBDII checker and if so, where is the OBD connector typically??

 

[Don S]

Re: Ignition circuit fuse blowing

One friend suggested for the heck of it to hook up to the ECU and look for any fault codes. Does this Merc MPI use the standard OBDII?? Can I use my auto OBDII checker and if so, where is the OBD connector typically??

No, No, and there isn't one.

 

[rbezdon]

Re: Ignition circuit fuse blowing

Well, so much for that suggestion. Thanks Don.

Can I start and run the engine with the round connector disconnected from the helm using the jumper with fuse you suggested and jumping to the yellow/red to engage the starter as above??

 

[rbezdon]

Re: Ignition circuit fuse blowing

Good News, problem solved. My son found a pinched wire where the help control clamps to the steering cable under the dash. it was the purple/white which seems to be the "boat side" of the ignition switched 12V main power (purple with no stripe being the engine/power plant side of the ignition switched 12V main power). Spliced out the pinch and all seems OK now.