Alternator idiot light question

[Burkslaw]

2002 California Stone. When I turn the ignition switch from off to on the alternator idiot light does not illuminate. Turn it from off-on-off-on and it lights on the second "on". If I turn the switch on once and hit the starter it starts immediately, and the generator functions properly (as it also does if I turn it on twice.)
I think the alternator needs to be excited by the idiot light, but it charges properly whether I turn the key once (no illumination) or twice (idiot light illuminates), so the charging system is getting a tickle signal whether the light comes on or not.
There do not seem to be any loose connections, and the on-off-on thing works without fail every time.
Is it SOP to have to hit the switch twice before starting?

[Old Jock]

Checking the wiring diagram, it would appear that the Stone has the Ducati charging system and not the older Bosch.

The alternator is a permanent magnet single phase type, so it doesn't need any form of excitation to get it going, the permanent magnet within it does that.

It's not SOP to have it not light alternately AFAIK, it should illuminate every time you switch on the ignition, but I can't think why it's behaving that way.

I think the light is not that reliable anyways so no need to panic, but I'd go through the system checking the connections and ensure the RR is well grounded, many add an addtional ground wire to the casing and earth off onto the chassis. The 2 yellow wires coming from the alternator are (if their anything like the Sporti etc) connected via a plug that can also come loose fairly easily

That's about all I have, let's see if anybody else has better ideas or inputs

John

[Chuck in Indiana]

The alternator light on the Mighty Scura used to work or not work depending on phases of the moon, I think. I never did understand that..

[berniebee]

Agree with Jock, no excitation required to start this alternator. And the alternator light should come on every time.

Assuming that your oil pressure light does comes on every time you switch from off to on, that means the issue is not with the battery connection, ignition switch, light relay or fuses.
First an easy test for a potential regulator ground problem: Reproduce the symptom ( ignition on/light off)  and touch a test wire to the body of the regulator and to a bare metal part or bolt on the frame. If the light goes on, the regulator is poorly grounded. Clean the ground wire connections and regulator to frame contact and you're done.

If not it gets more complicated. I'm not familiar with the physical layout of this bike. I'm working from the circuit diagram, so it's up to you to find out which of my suggestions is easiest to perform.
Check the light blue wire that goes from the regulator to the alternator light. That light blue wire goes through a 10 pin connector.*  Could be corrosion at that connector. Sometimes the issue can be resolved by just unplugging and replugging the connector a few times which scrapes off the corrosion.  To test I would back probe the light blue wire at the connector with a test light. Again with the symptom reproduced, check for voltage. If zero, then the problem is upstream, that is, between the connector and the bulb. If 12 volts, the problem is between the connector and the regulator.  If it's easier, just check alternator bulb socket for corrosion and/or try reinstalling/replacing the bulb.

*That connector may be under the tank or near the headlight. Like I said , I don't know the physical layout.

[LowRyter]

when the alternator went out on my EV, I didn't have a light.  Confused me.

[Chuck in Indiana]

Agree with Jock, no excitation required to start this alternator. And the alternator light should come on every time.

Agreed, but the Mighty Scura's light generally only worked after coming off an interstate run. (?) I trouble shot it a bit, decided I didn't care, and paid no attention.

[Kiwi_Roy]

https://www.thisoldtractor.com/guzzi007/schematics/2002_Stone.gif
All good suggestions I would start with a decent ground connection from the regulator case to a timing cover bolt
perhaps use a 1/2" strip of aluminium with liberal application of grease to prevent corrosion.
The schematic shows a black wire from the case to battery negative but the path from main battery ground through the engine is better.
The Red/Black feed from fuse 4 to the regulator through the relay (22) is what turns the regulator ON and it grounds out the generator light.
So with the key turned ON you should see +12 Volts on the Red/black and if you ground out the pale blue wire the light should turn ON