Re: 1983 50 hp Johnson Rectifier test results

[Don]

Ralph-
When you said "0", did you really mean infinity? These terms get confusing and cause confusion….
In any event, you will probably need to test the resistance on a fairly high scale, using the low scale would show an open (infinite resistance) in both directions when testing each diode. You later mention using the "diode test function" and beeping.
In any event, like Frank says, there are six diodes that each have to be checked in two directions.
Test three of the diodes by checking between each yellow rectifier lead and the red rectifier lead. You should see infinite resistance in one direction, and less than infinite resistance in the other direction.
Test the other three diodes by grounding one lead of your ohm meter to the block or rectifier case (if you have removed it), then connecting the other ohm meter lead to each of the yellow leads one at a time. Again, you should see infinite resistance, then less than infinite when you reverse ohm meter leads on each of these three diodes.
So, you are checking six diodes in total, but doing twelve resistance tests because you are reversing ohm meter polarity on each diode…
Keep in mind that this is only a four amp charging system, so you will not see much of any voltmeter deflection at low speeds, especially if you are running other accessories. You probably won’t see much over 13 volts when you run at high speeds. Keep in mind that a bad battery, poor connections, inaccurate voltmeter can affect what you are seeing even though the charging system is working as designed.
You could connect an ammeter in series between the rectifier red lead and the red/hot lead it is connected to on the terminal board. You need a fairly sensitive ammeter that can show low amp readings clearly. You would connect the positive lead of the ammeter to the red rectifier lead, the negative ammeter lead would be connected to the red/hot battery lead on the terminal board. Please be very careful not to let these hot leads touch ground. Again, you wouldn’t see much at lower speeds, but should see 2-3 amps once you get the RPM up.
It might be simpler to just connect the ammeter between the engine’s positive battery lead, and the positive battery post. I know, I know, usually it is a no no to pull the positive engine battery lead off the battery when it is running. But, it won’t hurt anything to do it on this charging system.
Needless to say, you must start the engine first. PLEASE do not connect the ammeter between the engine positive lead and battery positive post then try to crank the engine, your ammeter won’t like trying to get a hundred amps squeezed through it while trying to run the starter motor!
So, again, start the engine, then remove the engine positive lead from the battery while the engine is running. Now connect the positive ammeter lead to the engine’s positive battery cable, the negative ammeter lead to the positive battery post, then check output at higher RPM.
Let us know if you don’t see alternator output, then we can go on to check the alternator windings and connections….
PS- are you sure you have the yellow leads properly matched up between the rectifier and alternator windings?
There are three yellow leads that have to be matched properly, oftentimes hard to see…
Yellow (no tracer)
Yellow with a grey tracer
Yellow with a blue tracer
Again, these tracers can be hard to see, make sure the yellow leads are properly connected between the rectifier and alternator leads….