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I've been recommissioning a 500W (1978) and have completed about 200 miles in short(ish) test rides. With a fully charged battery it starts easily on the button but no charge is reaching the battery - no change in volts across the battery when the engine is running. Checked the alternator output - low values (10v approx) on the yellow leads and not halved when testing yellow/red. As I understand it that should mean the stator coils are the issue. Looking at the stator I think it's been rewound, no signs of damage and pre-insulated copper wire. I've look at several of the older threads on this subject but many are beyond my basic electronic knowledge.
Are there other tests I can carry out to confirm the condition of the stator?
Could it still be the regulator? Could I swap with my 1977 3.5 regulator?
Any recommendations of who could take a look/repair?
Anything else?
In a bit of a rush as had been planning to take the 500 to the IOM!
Thanks in advance
Andy

Have you measured the resistance across the coils and to earth? The wires coming out of the coils look bare. Without a closer look, it is hard to say. The blue book does have a diagnostic page on charging problems.

Have now had a reply from the previous owner (thanks Pete) - the coils were rewound by Rex Speed Shop. Copper wires are pre-insulated (clear coating)

Had some further thoughts..... primary check of the regulator is OK (yellow wire terminals to casing). Looking at the terminals below the fuse box the insulators in the two red wire blade connectors show signs of melting - red from alternator and to large fuse, see photo.
Could this mean it's the regulator after all?

Hey there,
10v is very low on the yellow to yellow wires on the alternator, I recall 29v or so was fairly normal.
Sorry if I am teaching egg sucking Granny, but make sure your meter is on the AC range not DC.... DC will give a lower bogus reading.

The 3.5 and 500W systems were similar, so worth testing the 3.5 output to compare.
- there are some after-market regulators fitted by some owners which do not use the red centre tap wire, worth being aware of that.