Been fiddling with the electrical system on this last night. I'm trying really hard to not throw in the towel on the dynamo and just fit an alternator. No wonder so many got converted to an alternator and the car industry changed over so quickly once they became affordable. Electromechanical units may be nice in that they are easily adjusted, but solid-state units don't go out of whack so easily like these do.
Essentially on this car, you have to have the engine running at above 2k before it's charging rather than discharging and even then it's only putting back around 2 amps. Above 3k it charging properly at around 10-15amps. So the dynamo itself is working just the control box isn't controlling properly.
One of the things I noticed was the contact for the cut in and out relay was bent far out. You adjust the cut out voltage by bending this but you could see it only cut in at high revs when on the car.
After a bit of fiddling on the bench and using an old coil to provide some load, I got the cut in to just about 13v (spec is 12.7v to 13.3v) when slowly winding up the volts. Cut out is at around 10.8v (spec is 9.5v to 11v). Higher cut out than I'd like but I was struggling to get a good mix from a decent cut in and out. Given the cut in is adjustable with a cam, I put that value as more important than the cut out which is adjustable by bending the contacts.
I need to check the operation of the voltage and current regulator parts of the control box. However these rely on adjusting the field windings to regulate the power the dynamo is generating. Something not easy to replicate on the bench as it's quite a dynamic thing to copy with a fair bit of interrelationship between the different elements of the circuit.
Then I turned my attention to the fusebox. There was an interesting mix of fuses in there. One was rated 35A on the casing but that must be continuous rather than peak, while being a slow blow going by how chunky the fuse link inside is.
As far as I'm aware, on this age car the standard pretty much was 17A continuous and 35A peak. The circuit for the fuse above fed the Horns and Main Beam. So quite high loads but should be within the capability of a 17A fuse.
Second fuse was a lovely Lucas branded original with a paper insert. Unfortunately one of the end caps twists and that is asking for trouble now I've removed the fuse. Any movement on those caps risks snapping the fragile fuse wire and at the tops where you can't see it.
The spare fuse was a Lucas 25A fuse that was partially filled up with either oil or old grease! All three were replaced with new 17A/35A replacements.
I cleaned up the contacts on the fuse box itself as best as I could with it mounted in the car.
Then gave it a wash as it was filthy from garage dust.