40hp Johnson blows 20a fuse when key is turned

[fherb24]

Good evening all,
I have recently inherited a '97 sea nymph with a Johnson J40TPLEEA, it's a tiller with the key switch on the side of the boat and the ignition button on the motor itself. The engine was running fine and suddenly began blowing the main 20a fuse every time the key switch was turned. It blows instantly. After a few hours of tinkering (I'm pretty novice with this stuff), I discovered that when I remove one of the black wires (with a little yellow on it) from one of the small starter solenoid terminals, it will start and run just fine. The trade off is the kill switch no longer functions. I'm wondering if the fix is as easy as replacing the kill switch, or if there is potentially something more involved, as it seems maybe that wire is more than just the kill switch ground. But without a wiring diagram, I don't know what else is potentially attached to it. I have identified the wire in question with a blue arrow in the attached picture. Any thoughts on fixing this?
Thanks!

 

[jimmbo]

Welcome to iboats
Odd that a Ignition Kill Circuit would have Voltage on it. Most I have seen work as Grounds to kill the Ignition. Of Course, I am not thinking of an ECM controlled Engine, which this motor might have that...
I would be checking the Key Switch and Wires attached to it
Since you Inherited it, you don't know the History of the Motor. I would suggest you attain a Factory Service Manual and using the Wiring Diagrams, check to see if it Wired as it is supposed to be. And as you are checking that, you can also be checking for Frayed Wires, Pinched Wires, Shorted Wires, etc

 

[Crosbyman]

hard to tell but the yelllow red is typically the key's START control on the solenoid with the solenoid black being ground... your extra (black-yellow) wire you took off is a ground return supply back to a kill circuit which you disconnected .

being a solid ground source is it usually not a problem but any B+ getting crossed over to hit would blow the fuse at KEY ON .

this can happen anywhere the ACC power (usually purple) provided on KEY ON gets grounded either due to a defective key (internal problem) or wire chaffing between the purple B+ at key ON and the black wire you disconnected.

I would closely inspect all the wiring.. try spreading or probing around to see if the fuse stops blowing

a small 12v filament bulb inserted in the fuse holder with turn maximum bright at key ON with the ground condition present. ( saving blown fuses)

Simply wiggling probing the wires or harness may suddenly reduce the brightness indicating the solid ground has been discovered.

 

[fherb24]

Thank you all for the input on this one, I sincerely appreciate it. Here's where I am at:
1) I ordered and installed a new key switch. This did not solve it.
2) I probed and wiggled every wire in there and did not solve anything doing that either.
3) I tracked down a manual and found what I think is the correct wiring diagram (attached here). From the looks of everything, it is wired as it should be, and everything looks factory original. I'd have to guess there's less than a hundred hours on this thing, it looks pristine in there.

4) Looking at the wiring diagram, I couldn't figure out how that wire I removed at the solenoid has anything to do with the kill switch. So I messed with the kill switch and it turns out that was just a little sticky, it works just fine with that wire removed, I was mistaken.

5) Which leads me back to that wire....from what I can tell from the wiring diagram (again, pretty novice here so correct me if wrong), that wire has connections to the oil tank, VRO pump, and system check gauge. Does that look right? If yes, any advice on next steps?

 

[fherb24]

Here's the diagram

 

[Crosbyman]

diagram aside...
the usual wiring is a fused 12v off the B+ to the solenoid where the battery B+ connects.
it gets +sent to te key switch B+ post and at key ON B+ leaves the switch on purple to the ignition and accessories. ...incl power to VRO etc...

first thing to do is remove all accessories to see if the fuse still blows if not find the bad accessory.

 

[racerone]

That black / yellow does not belong on the solenoid.

 

[saltchuckmatt]

I couldn't pull up your diagram but here it clearly shows that wire is NOT connected to the solenoid.

https://maxrules.com/graphics/omc/wiring/40_50_UFI.jpg

 

[Crosbyman]

A red B+ off the solenoid is fused then goes to plugs for accessories , front key B+ post, etc... and may go to trim switches in some case. the full amp wires feeding the trim motor blue-green is tapped off the solenoid and NOT FUSED... relays are directly fed full amperage and would not cause a blown fuse.

Disconnect all loads and plug them back one at a time. Ttrace down all loads using purple reds... or any extra wires from a week-end mechanic.

The blowing fuse needs to be isolated from each load as you progress towards the faulty one (as you reconnect each one ). When it blows you found the problem load.

blowing fuse with no attached load means a groundded wire past the fuse location otherwise smoke would show up !!! inspect closely till the problem is found




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