Hi all. Just prior to winter last year the generator light lit on a long ride and after I made it home (70 miles) the battery was discharged to the point where it wouldn't start the bike. Since it was the end of the year I just parked it until now. This is a 1977 XLT.

I have the service manual and followed the procedures for polarizing, tested for generator light ground, and am going through the generator test procedure using a 0-30-0 ampmeter. I had been getting little to no amps on the initial tests I performed. I pulled the generator and found it to be quite dirty. I took electrical cleaner and cleaned it thoroughly and also replaced the brushes (although the old ones didnt' look that bad.

I put it back together, repolarized, and the generator light now goes out at right around 1000 rpms, but it still isn't charging the battery. I don't see any increase in voltage at the battery at all when running.

I retested with the ampmeter and I am getting NEGATIVE 20 amps when at 2000 rpm. Does this sound right? I checked and rechecked the test procedure and I think I am doing it correctly. I would've thought that it would have read positive.

I have searched quite a few posts on here regarding the testing and I think I am doing it correctly.

I am about to pull the generator again to see if I could have connected something wrong when I had it apart. I am pretty **** with labling everything but I guess I could have messed up. But thought I would run it past you folks first.

Thanks and ride safe,

Jim

 

Since you have a 1977 model I am not sure if I can offer any help.
But I shall try.

There is a possibility that the generator light is grounded. Were that to happen, the light stays on and the charge from the generator goes to ground rather than to the battery.

The ammeter should not be showing a negative 20 amps. Are you certain that when you do the output test that you have the positive post on the ammeter connected to the 'A' terminal on the generator and that you are momentarily touching the negative post on the ammeter to the positive post of the battery?

You need to get the generator output showing a '+' output first. Then it may or may not charge the battery. If it does not, then look to the voltage regulator as the problem.............. pg

 

Thanks for replying PG. Yes I thought the same thing as to if i was testing properly. I confirmed and I am. I think I have a couple of problems going on here and after a retest I am getting the gen light lit when testing for ground. So I have something to investigate on that side. Maybe grounding out on vibration.

The point about the gen light ground, I understand that that will affect the charging system. But, is it even in the picture during the gen test with everything disconnected?

This is a new china amp meter that I bought from autozone just for this testing. Would be interesting (although not surprising to me) if its faulty...now wouldn't it.

 

Maybe with everything disconnected the gen light is not of concern, but it is something you want to make sure it is not grounded with everything hooked up. This will prevent the generator from charging the battery if it is grounded.

As for the ammeter,,,,,,,,,
A few years ago an ammeter that would measure DC current was somewhere in the $600 range. Common to find an AC ammeter for $50 or so of course, but that will not measure DC amperage.
So maybe the Chinese make one today that is affordable.
This is what I use.............


pg

 

if it was not polarized wouldnt showing a - instead of a positive be an indication of that???--------i dont know that is your problem just wondering outloud....

 

Thanks PG. I am using the gauge similiar to what you pictured. Just got back in from retesting and still showing same result. Again - reverified I am doing the test per the manual and other posts on here that I have seen.

Yep. I have repolarized each time I disconnected. I guess my next step is to remove it and find somebody to test it and the regulator just to rule that out. That may be a while since I am busy right now. But I will post what comes of this when I can. Not giving up just getting a little frustrated. Sometimes I find it best to just stand back and think about it awhile!!

Thanks everybody. And if you should think of anything else let me know please.

Jim

 

Hmmm, you first had the gen light burning and the battery went dead riding it home.
Then you took apart the generator and replaced the brushes.
After that you said the generator light goes out at 1000 rpm. (That sounds like it is putting out some voltage)

But you said it did not charge up the battery?
Next you connected an ammeter and found that at 2000 rpm the generator output was (-) 20 amps? Of course the (-) should be a (+).

You seem like you have followed the directions closely, but let me ask you this:
How much dis-assembly of the generator did you do?

Is there a chance you switched the brush wires?
One brush is positive and the other is a negative.

The positive brush has a wire going to the 'A' terminal on the generator.
The other brush is the negative brush and it goes to ground.
That is the only thing I can think of that may be connected wrong.
Probably not the case as you seem to have been careful, but I just had to ask.
Keep us up to date on the progress when you get back working on it.
pg

 

Well I pondered and pondered and pulled the generator back out. I did find everything connected properly. One thing that I did find was that the wire from the armature (inside the generator below the "A" terminal had what looked like wear on it (hitting armature?) and the lug on that fitting was turned and touching the case. Sorry for poor technical terms. Fixed that and put it together. I get negative 10 amps until I rev it to around 2500 (according to the tach) then it goes to positive and bounces between 10-15 amps. I checked the battery with engine revved and am getting 13 volts which I wasn't getting before. Getting quite a bit less with lights on though. With a friend that had a trailor on standby, I took it out for 20 miles ride. Came back and checked battery voltage and it appears to have held. Left with 12.3 came back with 12.5. So I think I may be close to having it licked. Doesn't explain why it fails the generator light ground test. The thing is hacked pretty good by previous owner. It really needs to come apart and be rewired, but that ain't going to happen until retirement.

I have to say I know a lot more about generators now than I ever did before.

Well....on to the honey do list now. Thanks guys.

Jim

 

I believe you succeeded in grounding out the generator with that lug from 'A' terminal touching the case. The 'A' wire is a positive. If it hits the case, then it goes to ground.
So, I think you have found your problem.
The generator is good as long as it is putting out 10 amps or more. Yours does now.
And, you are getting 13V at the battery which tells me your voltage regulator is working too.
Life is good! Let us know if there are future problems......... pg

 

This is very common problem at certain years generators... you were lucky that regulator didn't broke. About those technical terms, you made it understandable even without them :-)