Tach Trouble

[pelican]

Originally Posted by jwclbi

Hello, I have 1998 225 EFI Mec, trouble is the tach is intermittent. I removed the tach cleaned the connections, no different. Friend of mine has a new one in the box so I installed it with same result. Is there a "sending unit" for lack of a better term, somewhere on this engine. I looked for a couple minutes but couldn't really see much. Any thoughts would be great, thank you.

that motor,it has 2 regulator rectifiers - back of the motor - swap the grey wire with the other rectifier - it's probably the rectifier


grey wire isn't "hot feed" - grey wire is tach signal
purple wire is ignition
black is ground

not uncommon for those to go bad

check charging system - make sure it's working properly

the high output charging systems,they use 2 regulator/rectifiers

[jwclbi]

Here is a picture

[flyingfrizzle]

Tach diagram:

http://boatinfo.no/lib/mercury/manua...3lit.html#/158

Gauge arrangement:

http://boatinfo.no/lib/mercury/manua...3lit.html#/148

Engine harness:

http://boatinfo.no/lib/mercury/manua...3lit.html#/172
http://boatinfo.no/lib/mercury/manua...-3lit.html#/98

The 225 3.0 is different than the 150-200s of that same year with the 40 amp system dual 20 amp rectifier boxes (looks like what you have pictured in your post) The 3.0 will have an alternator and the grey wire will come off of the box shown as #34&35 in the manual provided in the link above. Sounds like you could have a corroded wire or connector. Check all the connections in your harness to make sure they are clean and well connected also.

[gofastsandman]

Originally Posted by pelican

that motor,it has 2 regulator rectifiers - back of the motor - swap the grey wire with the other rectifier - it's probably the rectifier


grey wire isn't "hot feed" - grey wire is tach signal
purple wire is ignition
black is ground

not uncommon for those to go bad

check charging system - make sure it's working properly

the high output charging systems,they use 2 regulator/rectifiers

Tomato