I took my boat out yesterday. It ran fine, but my depth finder which is connected to the same battery as my motor, started flashing "WARNING VOLTAGE TOO HIGH" and my tach was running up to 7000 rpms, at 50 mph. and the gas gauge was really fluctuating.
details: 1979 Merc 150 v6.

everything else seemed to be fine. Not sure if something is going out on the motor, or a battery problem, or a depth finder problem (don't know why that would effect the tach.) ? ? ? ?
Please give some advice or suggestions on where to begin or what to check.
Thanks in advance...

Ricky, you need to join the www.screamandfly.com forum. You can post this question to the guys who live and breathe Outboards.

That is one weird problem my Friend. Good Luck with it.

The tach feeds off of pulses from the stator. Tells me with high voltage that your stator is bad but you might change the rectifier first to see if it is the culprit. These early Mercs use only a rectifier to control voltage and they do`nt work well with a deep cycle battery. Double check everything connected to the main battery for + and - Has stator been changed recently because if you get the wrong amp stator and or amp flywheel combination it will cause this. Good Luck

Ricky, That system only has a rectifier not a regulator. That means that the volts are not regulated to a certain spec and then stops at that rate. I have seen unregulated voltages as high as 18-19v. What is happening is the newer electronics are synsitive to high voltage spikes and it will warn you.I don't think you have anything wrong with your charging system, unless it is really overcharging, then I would have it checked out by a tech.
Now the rectifier could be bad allowing for the tach to not be accurate, as Gary indicated. If everything checks out ok then you can wire the depthfinder to one of the trolling motor batteries. This is ok but you might get some interferance from the trolling motor when it is on.

Tommy Yetts
Rockwall Marine

Tommy; I appreciate the info, I have two depth finders, one is on the trolling battery and the other is on the cranking battery. It would be easy to put them both on the trolling side. My tach has always ran higher than I thought it should. but not that high. How can I test the rectifier?
Thanks again for the help.

Ricky, I've had similar problems with an older Evinrude and found help on the bassboatcentral.com website - go to the forum for your engine and search for rectifier.