I'd been away for a fortnight's holiday (leaving the Red Special behind) and when I got back it was reluctant to start - and it's usually absolutely immediate.

Then last night coming back from dinner with friends I thought the headlights looked dim. This morning it wouldn't start: no click from the solenoid at all. I jump started with another battery, but after that the voltage reading at the battery was a steady 10v (!). We were very lucky to get home last night it seems.....

I am currently - hah! - charging the battery. That should tell me if it's a battery problem.

How can I tell whether it's the alternator not delivering anything, or a failed voltage regulator?

If it is the voltage regulator, I'll be a bit miffed, as it is the expensive solid-state version, only about two years old, and never maltreated. After all, it's been working fine up to now.

Where do I test, and how? Suggestions welcome.

My 2volts…

Requires a multimeter to see voltage.
Temp hook up a 12 volt lamp to alternator Exc spade connector and the battery 12 volt.
Start the car measure the volts on the battery, if over 12 volts Alternator is functioning.

Or

Borrow a regulator to swap with yours.

Solidstate regulators are reliable for many years .

Cheers
Peter

Peter: thanks.

Starting to check I think has shown me what the problem is. The "exc" lead on the alternator was very loose and showing signs of sparking/burning. Actually at first it was rigid, but as soon as i moved it, it became wobbly. It had maybe corroded into a set position that didn't conduct well.

I have cleaned it up and tried (not very successfully) to tighten up the connector - it's inside a fairly rigid plastic cover and not easy to bend into a more grippy shape.

With the car running I now have 14.5V at the battery, as against 13.4V when the engine is turned off.

Should I maybe think of clipping the end of the lead off and putting on a new female connector? There's not a lot of slack in the cable, though.

I vote for new connector. But how annoying to have to extend the wire somewhat for such a short distance.