Tach all of a sudden reads 1000 to 1500 RPM higher. I read that the gets a signal from the voltage regulator, counts pulses or something. Can someone please give me a better description on how this thing works.

You read correctly. The tach gets the signal from the voltage regulator and times the pulse to determine how fast the engine is running. Your problem could be a bad ground, bad connection, interference from another part going bad, tach going bad.....

Start by cleaning the connections on the back of the tach and making sure they are tight. You might also switch voltage regulators if your engine is a V6. On a Mecury, the tach lead is grey coming from the regulators. Funky readings may mean your regulator is going bad.

Artie

yes, it get's it signal there.

but, when does the tach read that much higher??? while your running down the lake? or even at an idle? all the time?

its actually called a rectifier and not a regulator

it could have jumped settings too

Thank you, stick. I've been sick for about 2 months, and it's starting to affect my brain.....

Artie

Thanks for the replies. The cranking battery seemed a little low also when I took the boat out, so I put the charger on it when I got back home. I took the boat out the next day. I had read that the tach should read 0 when the ignition is on but the motor is not running, and it did read 0. Started the boat up, ran around the lake, and the tach seemed to read correctly.

Did charging up the battery fix my tach problem or is something else going on?

Does the tach need a specific voltage to read properly?

Maybe my rectifer is going bad and thats why the battery was low?

I'd say your last statement is the most likely scenario. Another possibility, the battery cables weren't quite tight and you improved it when you hooked up the charger, although I'm not 100% sure that would affect the tach signal. In general, the battery voltage shouldn't affect the tach, but a damaged battery can look like no battery to the rectifier and cause it to fail.

Have voltmeter? measure the battery voltage with engine running (all accessories turned off), should be around 13 to 13.5 or more at idle, up to 14.5 (or higher if unregulated) at hi RPMs, but in any case should be higher than voltage with engine off. That'll tell you if the charging system is operational. Bad rectifier, will be the same or lower. Rectifiers sometimes start acting up intermittently before failing completely.

You can test the rectifier independently with an ohmmeter, if ya like I'll post a link to that procedure.

wallymart has an autoranging digital multimeter for about $25 that's good enough for general outboard troubleshooting and comes in handy for other stuff around the house.

I had the exact same problem with mine earlier this year. I changed the rectifier and the problem was solved..

Thanks. I have a multimeter and am a trained electronic technician, just don't a lot about boat motors. If you don't mind, please post how to check the rectifer.

I think it's time to put a Evinrude on that boat! I'm on break right now. he he

Definitely want to check the voltage output at the battery. Base line engine off 12.5 volts. Engine running may have to run the RPMs up should be 13 to 14 volts. Here are a few links. I might hit Granger Sun. am, will call u if I go.
http://www.maxrules.com/fixMERCwiringcodes.html

http://forums.iboats.com/showthread.php?t=190636

http://forums.iboats.com/showthread.php?t=190638

You should get back to work. You changed your name, almost didn't recognize you