Testing a rectifier.

I have a no. 8 awg wire from the neg batt. term bolted to the frame, not the floating ungrounded batt box. A no. 12 awg stacked on that connection point going to the reg. It has to grounded well. And it is not hooked to the floating ungrounded battery box. I do have the aluminum heat sink with the heat sink compound between the two items. See if all this sounds correct to you. On the reg. vr 115 I have the orange and yellow hooked to the load side of the switch " brown" wire. The black is grounded as mentioned. Green out to the left ungrounded brush on alt. Right brush is grounded through its mounting screw to the motor and the black hooked to it goes up to the neg. The rad. shack rects wired like the online diagram. I am going to go hook the rect to the switched brown. Does the metal body of the reg. need to be grounded? Have not looked yet to see, how the motor is grounded and I guess could that effect it? Thanks again Saga Stan lol

Yes, your wiring for the regulator is correct. The rectifier must not be connected to the switched brown. The rectifiers output only goes to the red wire, which is the supply side of the ignition switch, as well as the connection from the battery + (via the main fuse).

The metal body of the regulator (VR-115) does not get grounded.

The rectifier terminals do not need to be soldered. Some people do solder them, and that is fine. My rectifier terminals just use push on connectors, with heat shrink insulation........ the heat shrink helps to prevent them loosening. My rectifier terminals have stayed tight for about 5 years now.
 
I am going to hook the regulator to the switched brown. And leave the rect. unswitched on the big red going to the switch. I am going to take the grounds and put a in a copper mechanical lug machine bolted to the frame to make "absolutely" sure that it can't be intermittently grounding the reg. Took it for a short low rpm spin and was kinda weaving around getting the feel of the handling and it started running really rough. That almost put me over the edge. I checked the voltage and it was spiking up to 16 v. This has to longest ongoing thread this site has ever seen. Totally depressing me and this one thing is killing me. I feel like I could wire the rest of the bike off of the one line diagram but the alternator has been a prob. since I bought this bike in early October. Wow Now have to figure out what went wrong to make it run rough. Thank you all so much, you have to be sick of hearing from me and "same" dang prob. Saga Man Stan
 
Resurrecting this discussion mainly because there's a great amount of information here and I'm going crazy right now with a charging issue. I'm curious how relevant this information is to the '79 XS400?

I'm currently not seeing anything above ~12.6v no matter what RPM my motor is at.
When I jumped the green wire from my regulator (solid state, not a RR combo) to battery ground, I saw that I was able to get ~13.5v measured at the battery when I rev up. But this also seemed to put a load on the system and it was idling lower and I noticed battery voltage dropping during idle.

When I test (ohm readings) my rectifier it reads fine.
When my key is on I'm getting battery voltage from the brown wire on my regulator.

This is roughly my current wiring diagram (I keep testing things to try and solve this). https://imgur.com/a/8d80h6a





1. First charge your battery to at least 12.5-12.7V.

2. Find a really thin feeler gauge like 0.010" or 0.015" and hold it pointed down about a half inch away from your generator cover on the engine. Now turn the key on. If your regulator and rotor are working the feeler gauge should slap the case when the magnetic field is created in the rotor. If nothing happens or the magnetic effect seems really weak then go on to the next test.

3. On the solid state regulator models all you need to do is locate the green wire at the regulator plug and make a jump from it to ground. That bypasses the regulator and allows full battery current to flow through the brushes out of the rotor through the green wire to ground. That causes the rotor to make a stronger magnetic field which in turn causes more current to flow in the stator. If your battery terminal charge voltage jumps up to 14.5VDC when you rev the engine then the regulator or the ground connection for the regulator is your problem.

4. If nothing changes then it's time to check the voltage on the brown wire (It may be black on your bike) at the positive brush with the key on. It should be very close to battery voltage. The brown wire that feeds the brush gets its power from the brown wire at the key switch. Check the voltage at the three wire key switch connector while it's plugged in by probing from the backside of the connector with the key on. Again you should see the same voltage as the battery. If you do get full battery voltage there then repair the brown wire circuit between the switch and the positive brush. If not then the switch is either bad or the red wire from the battery is not passing the full current like it should. If that's the case then keep going back along the red wire, through the main fuse until you find the source of the voltage drop. No more than 0.3VDC drop is acceptable.

5. Once you have full voltage to the positive brush re-check the charging voltage to see if you're getting 14.5 VDC or better at the battery when revved to about 3,000 rpm. If you still don't have a charge then do the feeler gauge test again. If it slaps the case your rotor and regulator are working and you can go on to stator checks. If not then pull the brushes out of their holder and use an ohm meter to test the rotor. Measure the rotor first by touching the tester leads to the brass slip rings. Then take one lead and touch anywhere on the engine that's not painted. For the first test you should see between 5 and 5.5 ohms between the slip rings. On the second test between one slip ring and the engine you should see infinity on the meter. Any reading lower than 5 ohms on the first test or less than infinity on the second test means you have a bad rotor. Replace it. If it tests good then go on to the stator checks.

6. At the stator wire connector locate the three white wires. Use a voltmeter set on the AC scale to test the three possible connections between the white wires by probing from the backside of the connector. (The connector should be plugged together for this test) With the engine running at idle you should see about 10.5 to 11 AC volts (Not DC) on each of the three combinations of white to white that you make. If you get a very low reading on one or two legs then something is grounding your stator. If you have high readings on any of the legs (i.e. 16-18VDC) then your rectifier is bad.

7. If you got low readings on any of the stator voltage checks then unplug the connector and use your ohm meter to check the stator windings. Check the resistance between the three fabric covered wires (stator side) on the side of the connector. On each white to white connection you should read about 0.4 to 0.5 Ohms. If you get a very low reading on all of the three combinations find the single Yellow wire connector and disconnect it. Re-check your stator resistance. If the readings are now good then the yellow wire or safety relay are shorted. If there is one or more that still read low after disconnecting the yellow then check those legs by touching one lead to ground with the other on the white wire. You should see a very high Kilo ohm or infinite reading. If you get a low resistance check the stator lead pigtail to see if it is pinched by the cases or rubbed through on the frame. If that looks ok then your stator is shorted and needs to be replaced.

And that's about it except to say that dirty connections and worn brushes account for most of the charging system problems.
 
I found this over on this site https://www.denniskirk.com/learn/how-to-diagnose-motorcycle

To begin, you should first check for continuity from the terminal tabs of the connector and then see if anything goes to the ground. Set your multimeter to Ohms to check this. First, use the multimeter leads to check the resistance of the tabs by checking A to B, B to C and then A to C. The multimeter should read under 1 Ohm for all three (make sure to take into account the resistance between the leads). Readings over 1.5 Ohms are an indication that the stator is faulty.​

So when I unplug and do the first test I get ~1.2Ohms across all 3 checks. Not ideal but not above 1.5,


Next, check to make sure nothing is going to ground by connecting the red lead to the connector and the black lead to the negative terminal of the battery. This should be an open circuit and the meter should not read anything. If it does, the stator is faulty.​

Next check the meter reads nothing as intended.

Now, switch your multimeter to read AC voltage. To check for voltage, the motorcycle must be running and should be at about 2000 rpm. Then, measure the voltage from tab to tab, just like before. The actual number of the voltage is not terribly important. What you are looking for is that all three of the numbers are similar. If the voltage numbers are more than a few apart, the stator is faulty.​

I get nothing on this check. 0v. But if I jumper the regulator green wire to battery negative, I do see 0.1-0.4v as I rev up. But really almost 0v.
 
When I jumped the green wire from my regulator (solid state, not a RR combo) to battery ground, I saw that I was able to get ~13.5v measured at the battery when I rev up. But this also seemed to put a load on the system and it was idling lower and I noticed battery voltage dropping during idle.
When you grounded the green wire, that bypassed the regulator. Your increase in charging voltage means the regulator is bad. I'd replace it with a known good one and go from there. You might have other problems 'cause 13.5 is a little on the low side, but if what you're describing is correct, the reg. is definitely bad.
 
Here's how you check your rectifier...

 
Thanks. I get the same results as the video for the rectifier so it looks like that is ok. Time to hunt for a voltage regulator it sounds like.
 
Something else to keep in mind... per your diagram you presented, you're using a type "A" regulator and not the type "B." Keep that in mind while you're looking. Good luck.
 
I used this one. It's a Fiat VR-794. 15 bucks on Ebay. It's a type A so should work just fine for you.
 
@Jim by your own post here http://www.xs650.com/threads/how-do-i-test-my-stock-alternator.53079/page-3#post-564601 is says that '79 and older would be type B. But you're saying the image of the one in my wiring diagram is type A? So either the pervious owner did a modification or some '79's use type A?
Well first of all, I'm not familiar with the 400 model yrs, so I don't know what's supposed to be there. What I was going by was the diagram you put up that's showing a type A regulator. Are you using the correct diagram?

iZ5Vicu.png
 
Also.... you said grounding the green wire increased output. Unless the wiring has been totally hacked, a type B would have had sparks aflyin' if you ground the green... since it's a power wire. .... and output would have dropped to 0V.... and most likely blow a fuse.
So... unless someone has hacked the brown and green wires, it's a type A.
 
@Jim so I finally got around to buying that Fiat regulator you pointed me to. It took a while as I had to wait until I was stateside.

My understanding is it’s green to green. Red goes to my brown wire from the stator and also splits off to feed power in to the lights/horn/etc.

And the body grounds to the frame.
 
@Jim so I finally got around to buying that Fiat regulator you pointed me to. It took a while as I had to wait until I was stateside.

My understanding is it’s green to green. Red goes to my brown wire from the stator and also splits off to feed power in to the lights/horn/etc.
And the body grounds to the frame.
Correct as far as wiring colors, but just to clarify.... brown is switched power from the ignition switch. It goes to the red on the regulator for sensing voltage. It's also split to the rotor (not the stator) to power it. But yeah.... green to green, brown to red.
 
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