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1979 Evinrude 75 HP Alternator/Rectifier test?

M

MyFirstBoat

New member
I was told that this alternator should be tested since the battery isn't really holding a charge. Can anyone enlighten me on how this is tested. One person told me to hold the testor leads on the battery and with the motor off it read 12.58 and with the motor running it read 12.44. I read in a post the other day "that i can't find again" that the tester should be put on the leads of the alternator. PLEASE HELP!!:):):confused::confused:
 
(Small Rectifier Description & Location)
(J. Reeves)


On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.


The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:


One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue


********************
(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
 
It would be a good idea to disconnect the battery to avoid accidental shorts etc. There is no need for voltage as you will be checking for OHMs, not Voltages.
 
OK one last question before i go try this. Do i need to remove the wires from their terminals (screws) to check them all or can I leave it all hooked up while i test this?
 
I just realized, Joe, that your post was the one I was looking for from the other day. I appreciate all the info and will try all this in the morning.
 
Just thought I would update this posting. Turns out it wasn't a battery or an alternator problem at all. The starter bendex was jammed with the flywheel. Problem fixed.
 
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