Help repairing old motorcycle voltage regulator

[hotrodjohn71]

Hi Group, This issue is lengthy and detailed. If you read it all, I will be very very surprised. If you can help me, I will be excessively grateful. Grab a cup of coffee and thank you in advance.

I have a 1973 Harley Davidson Z90. These small motorcycles were made by the Italian company Aermacchi in the years when Harley was owned by AMF (late 60's into the 80's). They are an all Italian unit with a Harley emblem on them.

One day when I was about 15, walking home from school in 1985 I found the bike on a trash pile in a neighbors yard and asked if I could have it. I pushed it home and after about 30 years have got it running and its fun but I myself am much bigger now :0

My question is in regard to the voltage regulator. It is working as far as it charges the battery at about 14V in a high rev of the engine, but the aspect of the regulator which is to *cause a charge indicator light to come on whenever charging is less than battery voltage* does not work.

I have been obcessing over this for a couple weeks. There aren't many folks left who apparently are knowledgeable about the electrical portion- at least enough to say "Just change the regulator". But I have decided I want to at least know which component of the regulator is bad before I give up and buy another one (If I can find one).

Heres where most folks eyes start to glaze over. Mine would too if I wasn't so obcesed with this.

The bike is a 12VDC. The 'charge light' is a small bulb located by the speedometer, isolated from ground with 2 wires going to it. One wire (The positive wire) comes from one pole on the coil which is fed (+) when the ignition switch is turned on. The ground for the other lead to the bulb is supposed to come from the terminal "S" on the voltage regulator. When the engine is *not* running and ignition switch on, the regulator is supposed to allow ground to flow to the charge light causing it to light up- in effect letting the operator know that there is no charging going on and to show the bulb is not burnt out.

When the bike is started up, the power (+) from the alternator flows into the regulator and should flow through the S terminal to the 'charge bulb' and the bulb should go out.

So to my problem and my question. With ignition switch on and engine not running, I am not getting any (-) at the S terminal of my voltage regulator therefore not lighting my charge bulb. The bulb is good and the ground connections in the electrical system are clean and free of oxidation and the 'charge bulb' is insulated from ground (and will light if checked manually with test probes).

Question is, from looking at the schematic diagram I shared of the regulator itself, can you determine where and how (-) is supposed to get to the S terminal? Also where is the ground origination to S from? Frame? Generator?

In the manual which I supplied a couple pages, there are 9 tests to test the regulator. I tested mine multiple times and it passed every time with flying colors. I notice that there is a resistor associated with the S terminal(please see images of resistor). The funny thing about this resistor is that from my testing with a test light, although it passed the test , it seems like it only lets current flow through one way and not the other. but be that as in may, I dont know if its designed that way or possibly defective. The resistor appears to have "G.B.C Italiana 68 Ohms 1373"

The regulator is #4 on the diagram and the charge bulb is #17. The regulator has 4 inputs. 'N' for one of the 2 wires coming from the alternator, 'S' for the charge bulb, another 'N' for the second alternator wire, and +B for the battery.

If it is the resistor that is the issue , I would like to locate a substitute and fix my regulator.

 

[Martaine2005]

Hi, I am on a train ATM but can answer a question.
The ground is definitely the frame.
The resistor wont read only one way as you describe. However, it might if you tested it incorrectly by including either diode #5 or #6.
Have you got a multimeter?.
The ‘S’ is signal not aground. It’s half of an AC signal. The diodes are half wave rectification for DC to the bulb.
If all your tests are fine and prove a working rectifier/regulator, then you really only have two options. Either the Black or Violet wire to the bulb are open circuit.
May be the ignition ‘Black’ wire connected at #6 and coil.
Have you checked continuity of the mentioned wires?.

Martin

 

[Martaine2005]

Ground... Frame and engine block

 

[hotrodjohn71]

Hi Martin, first, thank you for your reply. I really appreciate it.
I have a couple of multimeters. One is analog and one is digital but they're not really high-dollar units. They seem to work good though.
I have been using a 12-volt motorcycle battery and one of those test bulb probes to do most of my testing. I isolated the charge bulb circuit (black and violet wires) both ways and it is good. The circuit itself is not shorting to the frame and the bulb lights up when circuit is charged. When the key is turned on, 12 volt positive runs to the charge bulb via the post on the coil. And I certified this by grounding the violet lead where it connects to the voltage regulator and the bulb lit up just fine.
I think you are correct about the resistor. I wasn't isolating it when testing it before. I think I was utilizing that diode 5 and 6(as you mentioned) when it would only light my probe from one side of the resistor.
But just now I tested that resistor(isolated) with my 12 volt test bulb and it will not light the bulb either way. Do you think that resistor is good or bad? And do you think that might be the cause for my issue? Thank you for clarifying that it is not ground that is coming from the S terminal but it is a signal composed of half an AC signal. That is something I had no idea of.
So now, I am at my bench and I just went through all those listed tests in the manual for the regulator again and it passed with flying colors.

 

[Martaine2005]

A 12v test bulb wont help you. Use a multimeter.

 

[hotrodjohn71]

Ok, what range should I set my meter to?

 

[hotrodjohn71]

When I set my meter to the diode symbol, then:
In test 1 in the manual I get .464 and .462
Test 2, I get no continuity
Test 3, I get .461 and .454
Test 4, I get no continuity
Test 5, I get .531
Test 6, I get no continuity
Test 7, I get .565 and .559
Test 8, I get no continuity
And test 9, I get 1.015

Now here's something strange. I isolated the resistor and checked it with my meter in the same mode as above. When I put the + lead on one side and the - on the other I got no continuity. When I reversed it, I got 1.015. I know that shouldn't happen with a resistor but is is.

 

[hotrodjohn71]

Oops.. I guess I used diode test mode.

 

[davenn]

@hotrodjohn71

the thread wont be deleted ... people gave good info

I will just close it