V 50 Electrics grrrrrrr!

[hooter]

Hi,  My 1985 V50 MKII runs like a clock but is not charging the battery.  Have had Regulator statically checked, OK.    Rectifier checked, OK.  Volt meter on dash is in the green but when I turn on the lights the needle drops into the red.  The igintion light goes out at 2000-2500 revs.
Now I need some expert advice.  To check the alternator is producing where do I place the multimeter probes and what should I get as a reading?
Where do I find a wiring diagram ?  The one I am using shows a black wire (earth) going from the D- terminal on the alternator straight to the regulator.  In reality I have a blue wire at the D- terminal that dissapears into the loom and is somehow black when it reaches the regulator.  The multimeter is showing some resistance (530) when I check each end of these wires.

Any help would be much appreciated.

[guzzisteve]

This one will do, page 115

http://www.guzzitek.org/gb/ma_us_uk/V35V50V65Atelier_041983%28GB%29.pdf

and earlier one--

http://www.thisoldtractor.com/mg_manuals/workshop_manual_v35_v50_en.pdf

You check the AC voltage on the 3 yellow wires going to the diode board

Batt light should go out at 1200-1500rpm

[Matteo]

More here.

http://www.thisoldtractor.com/guzzi007/sportissimo.html

[hooter]

 Thank you for the feedback. Very helpful.  Hugley time consuming checking everything but am determined to sort it. Might be in the market for a wiring loom.

[Guido Valvole]

An 85 V50 would be a Mk III, not II. Major differences, especially in the wiring. II has generic Bosch electronic ignition as used in the day by BMW, Ducati, Laverda, and who knows how many others. III went back to points, mostly out of cheapness. Do you have points or has someone previously fitted a Dyna or RITA? Sounds like maybe someone was in there and "fixed" something. Check the connections and grounds. Italian wiring is not necessarily better than British…
cr

[hooter]

No points on this bike.  It is a bitsa. 350 Imolla frame with v50 motor.

[Kiwi_Roy]

If it has the usual Bosch alternator check the Voltage across the brushes at idle, I think it should be close to 12

Describe the Alternator, regulator and rectifier with part Nos if you can read them, someone with a comparable system can take a few readings.
Include a link to the closest wiring diagram.

The V35.V50 manual calls out the Alternator as 0.35 Ohms I assume thats Yellow to Yellow not Yellow to Y
The rotor should read 3.4 Ohms, that would be right at the sliprings but at the terminals should be close to that also, say < 4
The Output is
4 Amps at 1250
13 Amps at 2100
20 Amps at 6750

As I said above the Voltage across the rotor brush should be close to 12 Volts, I wouldn't expect it to be < 10