Okay guys...I need some advice...I've never seen this before. I was on the lake today, and my accessory panel kept losing power...including my power switch, horn, bilge, livewell, lights, and both fishfinders. I check, and the motor fires right up, no problem. However, as I'm running down the lake, I look down and my voltmeter is MAXED out at 18v! Then, my tach starts jumping anywhere from 2000rpm to 5000rpm. Speedo, trim and fuel level worked just fine during all this. I disconnected my accessory power wires from the battery, hoping to avoid any damage...but it still ran at 18v with the screwy tach.

Anyone ever experienced this? Is there a way to test my alternator to see if its really puting out that much voltage, or if the gauge was just haywire like the tach? Or, is an alternator on a 115hp Johnson even capable of that much voltage???

Please help! Thanks in advance!

Another thought...I have my bow-mount Pirahna on a 1.5amp fuse...if the alternator were really pushing that much, wouldn't it have blown the fuse? Heres hoping for a short somewhere...

I am interested in an answer to this too. My voltmeter has been showing 18 plus volts for a couple of years now. It could be a poor connection, I just have not done any trouble shooting. It may not be related to Brooksido's problem.

Really? You've had the same problem? You know...it may have always said that, but I didn't notice until something went haywire with the electronics. Who knows...but I'm still confused on the rest of it. Anyone else seen the other symptoms my rig is having???

I would be checking the grounds on the panel. Needless to say its common to all.
B D

Not for sure but sounds a lil like your voltage regulator
may be going bad, let us know what you find, good luck

Since you have a J/E, it is probable that you have a water cooled voltage/regulator rectifier. It is wired directly to your VRO. The VRO can be the cause. I have seen in the past several VRO's starting to go out, and because of this they go to ground. pulling so much amperage that it makes the recharging system go haywire. Henceforth'..Tacks pegging out, volt gauges going off the face of the dial, battery pucking water out and terminals at the battery getting hot, so sevear that the electrical system shorts out and catches on fire.But NO HORN going off to signal anything wrong with the VRO. By the way, the tack is getting it's signal from the volt/reg. It's reading recharge impulses back to the battery, not sparks to the spark plugs. It has nothing to do with the ignition system at all, except that it uses the same ground. I just bought a 90 model 200 Johnson that the VRO did this, it now has a complete ignition/recharging electrical system, all but the wiring harness.$$$$$$
Oh yea, the nice thing is your depth recorders are designed and ready for low and high voltage spikes. The can handle the high voltage but when the volts drop below 9.5 they shut themselves down. That's why when your cranking battery gets a little low and you start the engine, your depth recorder turned off. You just sent all the amp/volts to the starter.

Like Mike said I have seen that too but had one last year it turned out to be the stator. You can disconnect the Vro electric plug and run test to check the voltage. First thing I always do is start disconnecting accessorys at the cranking battery one at a time trying to isolate the problem. Then same to the outboards electrics if not found at battery. Good Luck

Thanks for the advice! However, I do not have a VRO on this motor...I mix the oil myself. But I will definately try the accessories one at a time, and see what happens.

measure the voltage across the battery terminals with a multimeter, to see what's really going on--your alternator can put out 18v easy at WOT. tach gets its signal from the rectifier, so that's a clue that it's starting to go. some of the OMC's are unregulated, some have separate rectifier & regulator, some have a single component rectifier/regulator.

here's how to troubleshoot your rectifier:
http://forums.iboats.com/showthread.php?t=190636

had the same prob on my merc 200 96 model, was the voltage regs on the engine, changed both of them all went back to normal.

Where is the voltage regulator on my motor? I ordered a service manual online, but it wont be here for a few days. Took the cowling off today...just not sure where to look, or what I'm looking for...

Brook...Voltage regulator is on top of engine in the middle looks like a sqaure box about a 1/4 of it set up under the flywheel and yes you will have to remove the flywheel to remove the regulator...OPTI

I had some similar problems and then my my voltage regulator caught fire on the lake one day, had it fixed and no problems since.

Well...after taking some pics and getting a LOT of help from Tommy at Rockwall Marine, we discovered that I haved an un-regulated system. There is, of course, a rectifier to convert from AC to DC, but the voltage spikes up to 18-20 volts are apparently normal. Seems strange on a 115hp...but what can you do?

I'm thinking about adding a regulator. I don't have fancy electronics, but I do have two working fishfinders that I don't want to take a chance on. Does anyone know of an aftermarket reg that you can put just in-line with the battery cable? The one for the Johnson is about $110. Thats not terrible...but I'm just thinking...seems like it would just be a resistor of some sort. And, then I could just leave my rectifier in place.