TACH AND VOLT METER PROBLEM

[David Sandowich]

HERE IS A STRANGE ONE. I BOUGHT MY 85 CAT 30 LAST YEAR.GREAT BAOT. IT'S EVERYTHING I EXPECTED IT TO BE. AS ADVISED I MADE THE WIRE HARNESS CHANGE AND ADDED VOLTMETER AND IT HAS MADE ALL THE DIFFERNECE IN THE WORLD. ON THE LAST TWO TRIPS OUT FOR NO APPARENT REASON , ONCE STARTING THE ENGIINE ( WHICH STARTED UP JUST FINE ) THE TACK WOULD NOT REGISTER ANYTHING AND THE VOLTMETER WAS INDICATING ONLY 12 VOLTS VERSES THE USUAL 13 VOLTS. IF I KEEP MOTORING , THEY BOTH COME BACK ON.IT COULD BE 5 MIN OR A HALF HOUR. IVE CHECKED ALL VISABLE WIRING FOR POSSIBLE EXPOSED AND TOUCHING WIRES ETC.ANY ADVICE WOULD BE APPRECIATED

 

[James M.]

alternator

Dave,This sounds like it could be a wiring problem, or it could be the alternator. The tach is driven from an AC tap on the rear of the alternator. Usually attached to a yellow/orange wire with a ring connector, which corrode after a few years. If the volt meter is reading current, and your motor starts o.k., then you may have a voltage regulator or other alternator problem.I would take a look at the AC tap, if it's ok, then the alternator should go to a shop. Good luck.

 

[Ron Doescher]

Check ground wires

Do a thorough check of the ground wiring connections. When you install a voltmeter, it connects to the "hot" (positive) and ground (negative). That ground connection could be loose or dirty, causing an intermittent or high-resistance contact. It is possible that the tacho was affected by that installation.

 

[mike i]

RPM

At times it is necessary to rev the engine to get the alternator to start charging. No tach and battery voltage reading on the voltmeter would indicate the alternator is not charging. I rebuilt a Motorola alternator reciently with the same problem. I replaced the brushes, voltage reg., rectifier, and bearings. Problem gone.

 

[Terry Jack]

RPM, voltmeter soultion on C-28

I had the exact same problem. I did notice however that my hour meter was still working. Check every and cleaned every ground, replaced the alternator belt, checked the voltage from the alternator, had the alternator checked by a shop. Still not working properly. In fact I had the exact same symptoms you describe. I did find that if I'd rev the engine up it would frequently start to work. It finally got to the point this would not do it anymore.I have owned my C-28 since new in 1994.Finally I hired a marine electrician to help me. He found the wire from the alternator that sends the signal to the tachometer was hooked to the wrong side of the ignition switch. It was wired to the side of the switch where the glow plugs are wired. As far as I know it has always ben this way since the boat was built. How it ever worked is beyond me. Once he changed the wires around it has worked perfectly!!This is the second time my boat has been found to have incorrec wiring. When I forst go her the 120v wiring that show polarity was wired wrong. the rigger corrected it.