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Electrical Short.... Can't Figure it out.

T

TGBTG7701

Member
I have a mid 90s 40hp Mercury 4 cylinder 2 stroke outboard with an electrical short that has me puzzled. I took the boat out a few days ago, it ran fine, when I got home to flush the motor out, the 20 amp fuse beside the electrical box popped. I installed another fuse and just as soon as I turned the key it popped the fuse again. So I opened the cover to the electrical components, to see if there was a pinched wire, or anything burnt up or came loose, found nothing, I mean nothing. I took my Ohm meter checked each wire I could find to see if anything had went to ground, again nothing grounded that should not be. I took the plug loose that goes from my (throttle, electric trim control box) to the outboard motor, 4 of the pins on the engine side showed resistance to ground, that seemed like a lot to me. When I pull up a diagram of the components within the electrical controls on the engine it shows a voltage regulator, but I do not see one within the panel, I trying to eliminate things, but nothing is showing up. I appreciate any suggestions you might have.
 
Thank you for the suggestion, I tried that, but it is still popping the fuse just as soon as I turn the key on. I am about ready to take it to someone, I can not figure what it causing this. I took the stator loose and checked each leg to ground one more time, again I came up with nothing.
 
Are you running accys off of the ignition switch? Pull the cables off of the battery and check ohms from the pos terminal to ground with the key on and a new fuse. then start disconnecting wires one by one until you no longer have a short. Is your ignition switch in the control box or on the dash? Another approach is get a good schematic and just disconnect everything and one by one start connecting wires and check for ohms every time with the battery cables. Eventually it will slap you in the face. Normally it would be a bare wire somewhere shorting to ground run you fingers up and down every wire looking for bare wires, cracked or brittle insulation.
 
That motor will run with the remote cable disconnected, but you MUST hook up a hot wire from the charging circuit (and a ground) to the battery or the rectifier will be damaged. I suggest you do this--jumper cabling the motor to life--and see if that cures the problem. If so, the short is in the remote/ dash electrical system.

Good luck!

Jeff
 
I found the short, it was in the control box, something with the ignition switch. I purchased a new switch soldered and heat shrink the wires, did away with the quick connects. I am not sure why the switch shorted out, but a new switch fixed the problem.

Thanks for the help
 
Good job sounds like you may have dodged a bullet. If the hot wire would have shorted to the kill wire it could easily have cooked the powerpack. Do you have separate wires from the battery for the house wiring? Dont run any accys from the ignition switch keep them separate and always fuse any added hot wires to the battery at the battery that keeps you from lighting the wires up going forward in case of a direct short. You can use the hot from the ignition for the guages but connect the lights with a fuse box with a master power for the accys.
11666d1172161592-typical-wiring-schematic-diagram-instrumentpanelwiring.jpg
 
The only accessory I have connected to the switch is the tachometer power. I have a separate wire that runs from one of my batteries to a fuse block then to a series of switches. The ignition switch looked rough that came out, the guy I bought my outboard from freshen up the mechanical parts in the control box, but not the electrical. I have a voltage gauge that runs off my fuse block, again not on the switch, I noticed I am running between 14.5 to 17.5 volts cruising at about 4k RPMs. The 17.5 volts seems a bit high, is that to high?
 
Anything over 15 volts can/will create problems what kind of battery are you running? Get a DVA adaptor for your volt meter it could be your rectifier regulator. Using the wrong battery can cook the stator and the regulator. What is the serial number of your motor?
 
http://www.marineengine.com/parts/technical_information/cdi_194-5279.pdf
This is the more expensive regulator but either way if your deep cycle is a maintenance free type battery you need to get a flooded cell lead acid type battery. The newer batteries store energy much more efficiently is why you get the higher voltage at high rpms. Another cure is to run a high amp draw appliance to use up the extra power produced when running at high rpms. A little 12 volt space heater or ice chest.
 
It looks like it may work but not a big fan of aftermarket parts especially with the high cost of the switchbox and stator. I would stick to OEM or CDI parts is it worth saving a few bucks now I wouldnt chance it myself. Others here may know how well that part will work?
 
Please help , I have a mercury 150 4 stroke , that has a electrical short that I can not find but will run a new battery down in 2 hours . Anyone have any ideals please email me. We are on Vac. And 800 miles from home and all dealers here are three weeks out.my email
[email protected]
Ll
 
An electrical short won't run a battery down. A short will either blow a fuse, trip a circuit breaker or let smoke out of a wire.
 
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