David’s Norton 850 Commando

I do love sorting out old Brit bikes, but that’s not to say it’s easy. Commandos in particular are pretty awkward beasts to work on electrically, with very little room – especially the Mk3s like this one, where there’s an airbox where you might otherwise stick a fuse box, horn, ignition box or even a coil.

David had bought the bike as a restored runner, and mechanically it was a really nice job. The loom, not so much. The restorer had adapted a standard loom, patching in a Boyer ignition and regulator rectifier using everybody’s favourite horror product – Halfords connectors. (I know Halfords don’t actually make these things but you know what I mean.)

The result was a bit iffy: the ignition ran direct off the battery, and the alternator didn’t charge. Not matter, I said. We’ll wire it all up right and take it from there. David also wanted to go negative earth, which I was grateful for. I build negative earth bikes all the time, and switching to positive earth once in a blue moon fries my head.

Fast forward a week, and I was out the front with the new loom, testing the charging. It was pretty feeble – about 13.4 volts. The charge warning light agreed: it stayed on even as the revs went up. On an older Brit bike this is often a sign of a demagnetized alternator rotor. But I didn’t think this was likely on a Commando.

I tried hooking up a different regulator rectifier. Presto: the charge voltage went up to 14.4 and rising, as the somewhat exhausted battery recovered from its electric starting efforts. David ordered a new Boyer reg rec (aka Powerbox), because the bike was already wired for it, and it comes with a charge warning light wire. Once that was fitted, we had a result.

It’s a beautiful machine, and now it should be reliable and crisp for many years to come.