Gen Light on when key is off

[Markcarovilli]

I posted this on the Convert board as well and thought I would put it out here as well and see what the thoughts are....

New to me ‘81 Convert and all was well until about a week ago. Out for a ride and got home - turned bike off and Gen light was on and wouldn’t go out.  I disconnected ground on battery and of course it went out and didn’t come back on when reconnecting ground. So I figured all good.

Went for a ride tonight and made a stop, turned off key an Gen light stayed on again. Started up fine light went out , but notice Neutral light is now on when running.

Got home and lifted ground again and light went out but now comes back on when I reinstalled ground.  So where to start?

I haven’t rooted around on anything yet and hopping for some direction.  Thanks in advance,

Mark

[Wayne Orwig]

I think that means a bad diode on the diode board, or a short somewhere outside the diodes. Likely a bad diode.

But then my brain isn't working so well this morning, the caffeine hasn't kicked in yet.
But I think that can do it.

[Ryan]

Yup.

[Markcarovilli]

So where is diode board located and would Neutral light being on be another issue?

[wirespokes]

The diode board should be located behind the right side-cover. Checking it out requires an ohm meter testing each diode, but that test isn't necessarily proof. Looking it over visually can be informative - burned spot, broken lead, cold solder joint - that sort of thing.

[acogoff]

     This thing.
     http://www.mgcycle.com/index.php?main_page=product_info&products_id=757

[ohiorider]

I have a used one you're welcome to swap in for testing, to see if it eliminates the problem.  I picked this up on the road returning from Utah in 2005.  Had bad info from shop owner.  The tech immediately told me I should have bought a rotor, since telling him how the GEN light was acting indicated an open rotor, not a defective diode board.  I'll drop it by your office if you want.  The BMW owner I bought it from said it had tested ok ..... he had it as a spare.

Label says
- BOSCH
- 0197 002 003
- 020 
14V 22A

Bob

[Markcarovilli]

thanks guys and Bob - I'll get it sorted...

Mark

[Kiwi_Roy]

Which of Carl's diagrams would more closely represent an 81 Convert?
http://www.thisoldtractor.com/guzzi007/sportissimo.html
I have looked at several and it would seem power to the light is switched by the ignition switch.

I'm not saying it's not the diode board just looking further.

[Markcarovilli]

I’m guessing ‘75 Convert USA...

[ohiorider]

Mark, this probably applies to M Guzzi as well as BMW Airheads with Bosch charging systems.  We are advised to temporarily remove the battery ground before removing the front engine cover, so that in the event we inadvertently ground the diode board to to the block.  Apparently the boards can be damaged if this happens.  Kiwi Roy, is this applicable to Bosch equipped Guzzis?

Bob

[jkguzzi]

Just a thought but I have had dash bulb issues with my Convert with bad or disconnected grounds inside the dash. There is a lot going on in there.

[Two Checks]

The diode board must be grounded in order to function, no?

[Wayne Orwig]

Which of Carl's diagrams would more closely represent an 81 Convert?
http://www.thisoldtractor.com/guzzi007/sportissimo.html
I have looked at several and it would seem power to the light is switched by the ignition switch.

I'm not saying it's not the diode board just looking further.

In this photo, the bulb feeds current on the light blue wire into '61' on the diodes, or D+ of the regulator. That feeds the bulb current out of regulator DF, to the field. Once the alternator starts spinning, the three small diodes on the left side of the diode board feed power to the '61' pin, and the alternator bulb goes out as no more current is pulled through it.

Now, imagine shorting out one of the large rectifying diodes on the battery positive side. Now, even when turned off, battery power passes into the alternator windings through the shorted diode, and out through the small diodes on the left, into '61'. That back feeds power into the alternator light bulb. The load of the ignition circuit and other things at the ignition switch pass enough power to light the bulb, with the key off.

Those schematics are great, but often have little glitches in them. That is the quick fix you can see I had to do on the diode board.

[wirespokes]

Looking at the wire diagram, I see no other explanation than a failed diode. And, yes, the diode board is grounded, but that has nothing to do with this problem. The current from the battery is passing through a failed diode, to the charge light, and then finding a ground through something else in the circuit. I tried linking the diagram, but for some reason it didn't reproduce well, so here's a link to the article it's in. It's a quarter of the way down the page.

https://bmwmotorcycletech.info/trbleshootALT.htm

[Antietam Classic Cycle]

Mark, this probably applies to M Guzzi as well as BMW Airheads with Bosch charging systems.  We are advised to temporarily remove the battery ground before removing the front engine cover, so that in the event we inadvertently ground the diode board to to the block.  Apparently the boards can be damaged if this happens.  Kiwi Roy, is this applicable to Bosch equipped Guzzis?

Bob

Bob - that only applies to BMWs, which have the diode board under the front engine cover. On Guzzis, it was first located just above the engine (V7 Sport, 850-T), then moved back beside the battery on the right.

[ohiorider]

Bob - that only applies to BMWs, which have the diode board under the front engine cover. On Guzzis, it was first located just above the engine (V7 Sport, 850-T), then moved back beside the battery on the right.

Thanks for the clarification, Charlie.

Bob

[Kiwi_Roy]

In this photo, the bulb feeds current on the light blue wire into '61' on the diodes, or D+ of the regulator. That feeds the bulb current out of regulator DF, to the field. Once the alternator starts spinning, the three small diodes on the left side of the diode board feed power to the '61' pin, and the alternator bulb goes out as no more current is pulled through it.

Now, imagine shorting out one of the large rectifying diodes on the battery positive side. Now, even when turned off, battery power passes into the alternator windings through the shorted diode, and out through the small diodes on the left, into '61'. That back feeds power into the alternator light bulb. The load of the ignition circuit and other things at the ignition switch pass enough power to light the bulb, with the key off.

Those schematics are great, but often have little glitches in them. That is the quick fix you can see I had to do on the diode board.

Great Explanation 

[Markcarovilli]

Wayne

That makes perfectly clear sense - you all have saved me a lot of time to isolate the problem.

Thanks all again -

Mark

[Kiwi_Roy]

Hold up a bit, Wayne gave you a perfectly good explanation of how it could happen, you may replace the diode board and it still doesn't work.
We don't know what wiring changes have been made to the bike over the last 40 years.

In the meantime you could test each diode with a multimeter, preferably one with the diode test function.
If you don't have a diode tester you can use a battery and bulb in series to test each diode in both directions.
Both ends of every diode are available at a terminal, current should only pass from positive to negative in the direction of arrow.

I am particularly puzzled why the light went out when you removed and replaced the battery ground, a shorted diode usually stays shorted.

Is the rectifier clean and dry?

[Markcarovilli]

Kiwi Roy

Well diode board was bad one of diodes cooked and it is back to where ot should be - thanks Bob (ohiorider).

I didn’t take it out yet but the Neutral bulb is lit with kickstand down, don’t remember it being on before - so where is Neutral switch and why do you need one on a Convert?

The Gen light comes on and off as it should so the analysis was spot on.....

Now to get the neutral light to go off.

Mark

[Kiwi_Roy]

Well done
One of the large pressed in diodes or one of the smaller ones, they can be replaced quite easily.
Does the convert even have a Neutral switch, if so it will be on the gearbox somewhere.
According to the drawing it does (25), Interlocked with the start relay, that would be important for an automatic I guess.
The Start relay contact shows fed through the ignition switch, not a good arrangement I wonder if a previous owner has changed that?

If it comes on with the stand down it's the stand light, most Guzzls had one.
The diagram you referred me to shows a weird arrangement (53) (54) I haven't seen that before, a Convert owner will have to explain that.
http://www.thisoldtractor.com/guzzi007/schematics/1975_Convert_USA.gif

[Markcarovilli]

It was not the original diode board as you can see from the photo - also you can see the solder actually let loose (that was the first indication when I saw a little bit).

So that “special board” is getting a rest. 

Mark

[Kiwi_Roy]

I don't know how they kept that cool without a decent heat sink, i'm not surprised the solder melted.
The regular Bosch unit should be an upgrade.
I think the resistor on the board was possibly to back up the generator light the Bosch Regulator needs/

[ohiorider]

Amazingly enough, my 1991 R100GS is still operating on the original diode board, 28 years and 159,000 miles later.  Go figure!?

BTW - Glad to help, Mark!  Thanks, Bosch!

Bob

[Antietam Classic Cycle]

Well done
One of the large pressed in diodes or one of the smaller ones, they can be replaced quite easily.
Does the convert even have a Neutral switch, if so it will be on the gearbox somewhere.
According to the drawing it does (25), Interlocked with the start relay, that would be important for an automatic I guess.
The Start relay contact shows fed through the ignition switch, not a good arrangement I wonder if a previous owner has changed that?

If it comes on with the stand down it's the stand light, most Guzzls had one.
The diagram you referred me to shows a weird arrangement (53) (54) I haven't seen that before, a Convert owner will have to explain that.
http://www.thisoldtractor.com/guzzi007/schematics/1975_Convert_USA.gif

The neutral switch of a Convert is in/on the cable - it's the same as the brake light switch on Loopframes and other drum brake Guzzis. On my Convert, I eliminated it entirely since I didn't want to have to pull in the clutch to start the bike and it's only other function is to make the warning light blink. Wired the starter relay up "normally" without the neutral switch circuit and removed the flasher for the warning light.

[Wayne Orwig]

It was not the original diode board as you can see from the photo - also you can see the solder actually let loose (that was the first indication when I saw a little bit).

Hard to imagine that works without a heat sink.