Having Charging and Tach Problems???

[bucchb]

Well, this 1975 Glastron came originally with a 1973, 150hp Mercury, with a "Trigger" ignition (with distributer).

I have put a 1981 HP Mercury with the newer style ignition.

From day 1 (last year) the tachometer never worked. When you turn the key on the tack goes to 2K and when started the tach just flutters around the 0 mark.

Also, it didn't seem to charge battery. So, using the Mercury procedure I checked the diodes and found that it failed test #2 with continuity from Ground to the Alt. Pins.

So, I replaced with a RS 25A rectifier. Tach does the same thing, so I suspect the tach is NOT compatible with this style ignition???

With a digital VM I get 12.5V at battery when off, and when running, I get scolling, unintelligable numbers. Could be I need to check with an analogue gage, but still does what it was with original diode.

Any I deas or questions?? Thanks, Bill

 

[jimg984]

Re: Having Charging and Tach Problems???

tach wire needs to connect to either of the two yellow wires on the recifier

 

[bucchb]

Re: Having Charging and Tach Problems???

Tough to see but, in both cases, (old and new rectifier) have tach (brown wire) with the yellow stator wire.

Stator wires look new, suspecting a new stator was installed at some point.

This is only problem, motor runs "like new" considering I replaced a piston, and did rings and bearings. In breakin now, and would like to have everything working.

 

[Chris1956]

Re: Having Charging and Tach Problems???

Is the tach a Merc one from 1973? If so, it may not be compatable with the newer ADI ignition. Youy might do a contunity test between the brown wire at the rectifier and the sender wire at the tach. it should have near zero resistance. Make sure the tach has a source of +12VDC and ground as well.

 

[bucchb]

Re: Having Charging and Tach Problems???

tach worked perfect with the older motor. Never worked from day 1 with the new power head.

Remember I get a 2000 rpm reading with the key switch on, and the tach flutters with engine running.

I have heard they are incompatible, but looking for someone who could explain why.

Also, make recommendations for picking up a used tach, that works.

 

[Chris1956]

Re: Having Charging and Tach Problems???

The older Merc Tachs were driven off the switchbox for the battery-CDI ignition. The newer ones are driven off the AC stator pulses. Nearly all motors have stators, which is why those tachs are now standard.

 

[bucchb]

Re: Having Charging and Tach Problems???

Hmmm, well then there must be some other problem. Maybe the stator?

I had the 1975 Mercury on this boat last year and had an issue with charging. I installed a RS rectifier on that motor the exact same way as this motor. That is to say, 2 wires from stator with a brown tach wire under 1 of them, a ground and the battery connection. Charged and had a great tach.