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1973 evinrude 65hp charging

First, connect a volt meter across the battery terminals and observe the reading. Then, start the engine and increase the idle rpm somewhat and observe the reading again. If the reading has increased slightly, the charging system is functional. If there is no change in the voltage reading, do the following.

Temporarily disconnect the positive lead from the battery to avoid any accidental shorts, then check the rectifier as follows.

(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

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Let us know what you find.
 
There are four diodes in the rectifier. They are connected as follows:
1. Between one yellow lead and the red lead
2. Between the other yellow lead and red lead
3. Between one yellow lead and case ground
4. Between the other yellow lead and case ground.

To test a diode, you need a continuity tester of some sort. My favorite is an analog multimeter, but a digital one might work if you know how to test diodes with it. Some digital ones won't work. Even simpler is a continuity tester that works like a flashlight.

Disconnect all rectifier leads Then you would connect the tester leads to rectifier leads as described #1. You should get either a high or low resistance reading.
Then swap the tester leads to the same pair of rectifier leads. If you got a high reading before, you should get a low reading now. And vise-versa.

Now you would repeat the test on all three remaining diodes. That's two steps for each of four diodes---a total of 8 test steps. You haven't tested the rectifier until you have done all 8 steps and each one must pass. And don't bother adding additional steps.

BTW, do NOT disconnect any rectifier leads or battery cables while engine is running. If you do, no need to test the rectifier--you just blew it!
 
mmr said:
What exactly am I looking for by testing the rectifier and what is the testing procedure for that?
Click to expand...

Whoops, sorry about that..... as follows:

(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.

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So it would appear the rectifier is out. I'm getting readings both ways so. By replacing the rectifier will that solve the problem? What am I looking at for cost and availibility for this part?
 
A reading in both directions indicates a blown rectifier.

What caused it to blow?.... Usually someone hooked up a battery backwards or hooked up a battery charger to the battery backwards. The rectifier WILL NOT tolerate reverse polarity.

Check the incoming RED wire at the terminal strip, BEFORE installing the new rectifier to make sure that the polarity at that red wire is the "Positive" (+) battery voltage.

If everything else in the charging system is as it should be, the rectifier replacement will put the charging system back in working order. You can check the cost of the rectifier on this website or via your local dealership.
 
Running it with the battery disconnected will also blow the rectifier. That includes loose or corroded connections that do not make secure electrical contact.
 
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