Charging System shorting out.

[cephas1981]

Hey guys.  I have a 1979 R65.  I have noticed the voltage light stays on when I ride.  The other day, the battery was dead.  I checked the alternator and it's putting off a charge so I checked with the manual and ran the test to check for a shorting wire.  I removed the negative cable and got voltage reading on my voltmeter when I connected to the loose negative cable and the negative battery terminal.  The manual says I have a shorting wire.  I have looked pretty thoroughly through the harness and can't find any shorting wire.  Do you guys have any suggestions?  Is there a "famous" spot where wires rub and short out?

[Bob_Roller]

First, welcome to the forum !!

You've got the possibility of three different problems with your charging system .

First could be worn out brushes that contact the slip rings on the alternator rotor, they get worn to the point, that the spring that keeps them in contact with the rotor can't keep them in contact, and then you get a glowing 'GEN' light .

Second could be  stator problem .

Third possibility is a faulty voltage regulator .

Then there's the possibility of a wire problem in the system, not a component problem .

With a fully charged battery, place the leads from a multimeter on the battery terminals, start the engine, increase the engine rpm's to around 4,000, your charging system should be putting out around  14 volts, if it's not, you know you have a problem .

If you get good voltage with this test, I would check the brushes and the springs, especially if the bike has accumulated a fair amount of mileage/kilometerage .  

[montmil]

Welcome to the herd, cephas1981.

I offer for your consideration the following article from Snowbum. His article is lengthy bur may hold the key to exorcising your electrical gremlin.  

http://www.airheads.org/content/view/177/98/

We like to see photos of what our family rides. Post up, amigo.

Monte

[cephas1981]

Thanks guys.  I'll let you know what I come up with.

[Ed Miller]

"I removed the negative cable and got voltage reading on my voltmeter when I connected to the loose negative cable and the negative battery terminal."

You got a voltage reading with the key off?  I wonder if one of the diodes in the board can fail in such a way that the battery current can leak out backwards through it.

How did you check your alternator output?  Bob's description is the method I use.

[cephas1981]

Ok, so I've removed all  the  connections to the alternator and still got a reading.  Then I removed the diode and the reading went down to next to nothing.  Hopefully that was it.

(How did you check your alternator output?  Bob's description is the method I use.)
I check the output directly off the alternator using the standard 20V setting on the voltmeter.  At around 1000 rpm's it read 2-3v.  And yes, the key was off.

I checked the ohms on the board with the settings on 200k.  Using the negative tester on the  tab facing up on the side and the positive on the three prongs in the middle.  From left the right it read: 20  24  22, respectively.  When i reversed the positive and negative, all the readings were 140  70  52 on 200k setting.  Does this mean the board is bad?