Electrical Problem Please Help

[DXTypeS]

I recently bought a 1980 CB750K, the bike only has been ridden about 100 miles in the past 8 years. I rode the bike home about 90 miles, the bike ran but was low on power. About a week after I had it home the battery was completely dead. I retrned it to autozone and was given a new battery. The bike is still not charging. it tests under 12V when running. I have searched the forums but have not seen anything about the turn signals not working when the bike is not charging. Could someone tell me if the bike has to be running for the turn signals to work and if it is not charging will this also cause them to quit working. I ran a few tests that I found online and the R/R seems good but if someone has a better way to test it I would appreciate it. What is the best was to test the stator coil or the rotor?

[Polymer-2]

The first thing to do is unplug and clean all charging system connectors then reconnect them using electrical grease available at any auto parts store. Bad connections are the #1 cause of charging system failures.
Check the alternator by disconnecting the large connector under the right side cover and measure the resistance between each of the yellow wires. Honda says it should be about .41 to .51 ohms but I have one that is actually 1.5 ohms. You don't want 0 or infinite resistance. Now check between each of the yellow wires to ground. There should be no connection (infinite resistance).
The rotor and brushes can be quick checked by measuring the other 2 wires. I believe they are black and white but don't hold me to that. The rotor itself should be 4.2 to 5 ohms and there will be some added resistance for the brushes. Less than that is a shorted rotor more could be open. It's best to pull the cover and measure the rotor directly at the slip rings. Also measure from each of these wires to ground and again
there should be no continuity.
If you find a shorted rotor then the RR is probably bad too. A shorted rotor will overheat and destroy the RR.

[DXTypeS]

all resistance between yellows is 0, is this indicitive of a short? or a bad r/r? Is it just a coincidence that my turn signals stopped workign at the same time?

[Polymer-2]

They should not be 0.
.4 to .5 isn't much so make sure you have a decent meter. Mine will show .1 just from the meter leads but 0 would be a short although that isn't likely on all 3. Follow the wires back to the engine and make sure they haven't gotten against the exhaust and melted otherwise pull the side cover and inspect and re-measure the stator. You should have the connector unplugged when making the measurements so the RR shouldn't be in the equation.
I've noticed that the turn signals often quit working when the battery is extremely low.

[DXTypeS]

Sorry I was measuring resistance between r/r and plug. Resistance between yellows from plug to stator is .4-.5 between all of them show zero when checked to ground

[Polymer-2]

If you have a good ohm meter and a variable DC power supply you can do a quick functional test on the RR.
Unplug the RR and at the connector measure from the green wire to each of the yellow wires then reverse the leads and measure again. You should have a low reading of about 5-40 ohms in one direction and a reading above 2000 (2k) ohms in the other direction according to Honda. All 3 readings should be fairly close to each other.
Now do the same thing using the red/white wire and the 3 yellows. Results should be the same as above.
If your meter has a diode range use it instead and you should get .4 to .6 in one direction and a very high if not infinity reading in the other. This tests the 6 diodes in the rectifier section.

For the regulator section make sure your power supply has enough current to light a test light. Put the 12v test light across the black and white wires on the 6 position connector. Now connect your power supply across the green and black wires on the 4 position connector.
DO NOT EXCEED 15.5V DURING THIS TEST!
Adjust the power supply to 0 then turn it on. Now slowly raise the voltage and at some point (probably about 10v or less) the light will come on. If the light comes on then the alternator should charge (if it is good). Continue slowly raising the voltage and the light should go off somewhere between 14 and 15v. This is the regulator cut out voltage. If it doesn't cut off then the alternator will overcharge and fry the battery.
Although this sounds long and drawn out, once you do one it only takes about 3 or 4 minutes to do the entire test.
Hope this helps.

[Polymer-2]

civicdxtypes wrote

Sorry I was measuring resistance between r/r and plug. Resistance between yellows from plug to stator is .4-.5 between all of them show zero when checked to ground

It should NOT be 0 to ground. It should be open.