Re: 1985 Evinrude 70 Tach not working
If you checked the rectifier as follows and it checked out okay... then indeed it is okay. Was this your test procedure?
The "Gray" lead which should be attached to one of the yellow leads of the rectifier... or to a yellow/gray rectifier lead if it exists would be the wire that leads to the "Gray" wire of the tachometer... or to the "S" terminal of the tachometer if no wires lead from the tachometer. Check the continuity of that "Gray" wire with a ohm meter from the tachometer to the rectifier.
Does the tachometer needle bottom out to zero when the key is turned to the ON (RUN) position (engine NOT running)?
The majority of tachometers have four wires as follows:
Gray = Sensor. (connects to gray wire leading to rectifier)
Blue = Light bulb. (connects to 12v source of light switch... voltage present only when switch is ON)
Black = Battery ground. (DO NOT connect to "M" terminals of ignition switch)
Purple = 12v (connects to ignition switch "A" terminal
(Small Rectifier Test)
(J. Reeves)
Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.
Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.
Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.
Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.