All the connectors were replaced by me not long ago and still look as new apart from a tiny bit of dirt.

I'll check the reg/rec and alternator later tonight.

The headlights only made the battery power drop at idle when the high beam was on, but yeah under load it seemed they made it drop significantly, so it could be a problem under load.

Forgot to mention I also have the Rick O earth upgrade kit fitted.

A guide for battery voltages:

Idle:

No lights 14.0 volts
Low beam 13.3 volts ( expect 13.0 volts with 55/60 watt headlight)
High Beam 12.7 volts

RPM to achieve 14.6 volts:

No lights 2000
Low Beam 2500 (expect 3000 with 55/60 watt headlights)
High beam 3500

I suspect a dropped phase somewhere then, shall get to it tomorrow now as I'm busy tonight.

I really need a better multimeter.

I got 580-600 ohms on the reg/rec test with infinity with it switched round.

Got 1.1-1.2 on all the alternator resistance checks too.

I need to get a better multimeter as mine takes a reading when it likes, not when I want it to.

A couple of extra tests. Resistance from yellow wires to chassis, infinite resistance. And with multimeter in diode mode, red probe on rect/reg yellow terminal and black probe on rect/reg -ve output terminal, infinite resistance.

Just re-done the tests using my new multimeter.

Alternator resistance: 0.4-0.5 ohms

Reg/rec negative multimeter to POSITIVE reg/rec output then multimeter positive to alternator input pins (must have done it this way round the first time): 550-560

Reg/rec test negative to negative and positive to alternator input: infinity

Yellow wires to chassis: 0.4-0.8 ohms (oh dear?)

Yellow wires to chassis resistance was with the rect/reg disconnected?

Yup. Measured with it unplugged, red probe to yellow wires and black probe to the pillion pegs.

"Yellow wires to chassis: 0.4-0.8 ohms (oh dear?)", stator to frame short not good. Maybe insulation failure on one of the yellow wire where they come out of the alternator cover that can be repaired, worth a look.

Aye, I haven't had a good look at the engine since I changed the oil a while ago, only had the seat unit off for these tests.

Will get a good look sometime this weekend.