Hey BC
My bike before this one was a 70 Commando. Everyone here is correct, if it has a starter, its a 75 MKIII 850. LOTS of cool stuff can be done to it these days. Mark Rambow at colorado norton works is kind of at the uber high end of stuff. Making new heads, developed a new breather, hydraulic clutch, all kinds of cool stuff.
As far as electrical goes...well, I just ditched the whole thing and built a new one myself. That way I knew what I was into. Best bet is to change the whole bike over to negative ground. This gives you access to all the modern electronic ignitions (I put a Pazon in mine), most of which will not run Pos Ground. I based my rewire off the attached photo (however, I didn't have to deal with the starter circuits), and pretty much refused to do chassis ground anywhere. I prefer to run a star ground from one central location, similar to what I do in my entertainment work. Sorry...star ground=all items in an electrical system grounding to a single common point.
Its really not too difficult. Adds up to about, oh, 8-10 wires travelling from battery box to headlight, about half as many travelling from battery box to tail light, and the 2 that have to snake down to the rear brake switch. I suspect there is a little more to the MKIII, given electrical start, and the fact that the keyswitch was (I believe) on the handlebars. Mine being earlier model, the key switch was on the front side of the battery box (I believe this was stock position). I used only 14ga wire on the whole thing, and 12ga for anything to do with ignition systems or the main headlight (this bike was DC headlight, which the Enfield threw me for a curve with its AC headlight).
Took me, oh, I think an afternoon of concentrated effort once I assembled all the parts. Switched it to a halogen at the same time. Real basic bikes there. Oh, and ditch the regulator/rectifier crap for some sort of all in one. I always shopped at oldbritts, but any of the other guys suggested here will have the right stuff too. I think podtronics make a good (if pricey) one. Been a while since I researched that stuff....but its all generally available. Realistically, all brit bikes shared parts and design ideas between them. Seems like that lame Lucas stator/rotor was on every damn bike for 30 years. 
Ok...attach picture and move on. I lifted this pic from oldbritts.com. Its a diagram of their version of an 850 Norton MKIII wiring harness for Neg Ground. Very easy to read too, kindly enough.
Good luck, and keep us informed. When I get a few bags of money and get all the stuff done on my Enfield I want to do, there WILL be another Norton in my stable.
Fantastic info Mr. Noisymilk! My mechanic thinks we should just tear the whole system off and redo it with negative ground, and I'm starting to lean in that direction too. I had been browsing through oldbritts.com but somehow missed this diagram so thanks! This will help me lots. We've been talking to the owner and it seems he might know even less about bikes than me (which is pretty bad
). This bike has already gone through 1 shop, where the mechanic gave up and sent it to us. Apparently it was complete, running, and then sat over the winter, and wouldn't start come spring. Whatever the last shop did to it they've really made a mess, I can forget about following any color guides.
If things get too expensive for the owner I just might inherit a Norton apparently
He came in the shop in his socks and sandels and we've decided this bike is way too cool for him.
Topic: My Norton mess.... help? (Read 8924 times)