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Author Topic:   Rectifier/Regulator frying
salty_dawg2 posted 09-10-2001 04:11 PM ET (US)   Profile for salty_dawg2   Send Email to salty_dawg2  
The tach on my '98 90hp Johnson recently quit, and showed the signs of bad rectifier/regulator (still getting charging voltage @ voltmeter, but tach dropped to zero from about 100-200 rpm when ignition switched from off to on), so I replaced rec/reg, and when I went to crank cold engine, the tach briefly registered while cranking, then dropped to zero when engine fired and ran. I'm thinking I fried the rec/reg, but as it's a relatively new engine with little "rat's nest" wiring on my '76 Montauk, I can't figure what could have done it. Does anyone have any ideas?
Bigshot posted 09-10-2001 04:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
The main thing that fries them is a bad battery connection. If you are running and the batt comes disconnected, it will fry.
reelescape1 posted 09-10-2001 05:03 PM ET (US)     Profile for reelescape1  Send Email to reelescape1     
Switching the battery isolator swith while engine is running is also a no-no. It sounds like a loose connection.
daverdla posted 09-10-2001 07:08 PM ET (US)     Profile for daverdla  Send Email to daverdla     
I just put a tach on my 100hp evinrude. Should be similar if not identical to yours. Look for three wires in a single connector. One purple, one black and one grey. The purple is ignition, black is ground and grey(might be grey with yellow) is the tach signal. Measure the voltage from black to grey with the engine running. I think it should be around 5 volts at about 2000 rpm. I recently posted the URL of the teleflex site that has the tach installation intructions and here it is again

If you can't locate the wires at the connector, disconnect the signal wire on the back of the tach and measure the voltage to ground with the engine running. It will at least tell you if the signal is there.

Whalerdan posted 09-11-2001 03:27 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I just went through all this, this summer. Tach wasn't working, battery wasn't charging. Replaced the Rec/Reg battery started charging but tach still didn't work. Went through all the wiring disconnecting plugs. The next time I went out the tach was working. Must have had some corrosion on some of the contacts. If it hadn't started working I was going to try bypassing the boats harness and haywiring right to the terminal board to help isolate the problem.

Might read through this too.

salty_dawg2 posted 09-12-2001 11:53 AM ET (US)     Profile for salty_dawg2  Send Email to salty_dawg2     
Thanks, all. I found my positive connector cable end at the battery looks really bad. It's possible (probable) this is the cause of my problems, as I might be getting some minuscule arcing that is enough to cause problems. I'm going to replace the connector & see if it helps. Of course, if I've already fried my rec/reg, I'm tachless. I have a voltmeter in the diagnostics mode of my depthfinder that is showing OK charging voltage, so I might be able to live without the tach for a while, or at least until my rec/reg and/or stator go bad...

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