We got an old model 420 as a trade in, earlier this year. I actually ran it myself as a go to work machine, for a couple of weeks when my car broke down. It had been used hard but ran OK. Then we gave it to someone as a courtesy bike, it came back wrecked, whether it was coincidence, or the people we lent it to, I’m not sure. It was completely covered in cow muck and the RH front lower A arm broken, fitted a new one. LH lower arm was found to be cracked, so welded it up. Then the battery went flat, checked and not charging. Tried a new voltage reg, no charge, checked the wires from battery to reg, OK. Stator resistance tested OK, but experience told me you can’t always tell. So whole back end off and new stator fitted. This is a pig of a job on the 420 as there is a frame crossmember behind the alternator case, you have to pull case backwards and then turn through 90 degrees to get it past the crossmember. Anyway, still no charge. After a bit of head scratching I consulted the manual, which I should have done first. Apparently, if one of the relays in the battery box fails, the bike won’t charge. How this works, I don’t know, the charging system is almost completely separate from the rest of the wiring, on every other bike I know. Anyway, plugged in a spare sub-loom with new relays attached, as we have had problems with them before and easiest just to fit the lot, as a test. Bike started to charge. Checked the wires in the box, severe rodent damage, not for the first time, as I had repaired those wires before. So, soldering iron out and repaired them again. Plugged old loom back in and still no charge. Swapped relays for new ones, no charge. Finally fitted the new sub loom with the old relays, and it charges. Moral of this story, on a 420, if it doesn’t charge, it could be one of those stupid battery box relays, or the wires to them, rather than regulator or stator at fault.