76 Commando 850 electrical issues

J

• Modern Norton Motorcycles

76 Commando 850 basket case​

Hello, a friend inherited an 850 Commando from his dad that passed away. Knowing that I've worked on a lot of bikes. He asked me to put it together for him. I may have bitten off more than I can chew, this whole positive ground system has my brain completely twisted. His dad was in the middle of restoring it and to his knowledge, nothing was mechanically wrong with the bike. Had the tins painted, new tires. Etc. I thinking this was a slam dunk to putting it back together. I threw a new battery in, hit the key, and nothing, no lights, horn, starter or spark. Where should I start? Please don't tell me to get a manual, I have 2 for the bike and they are vague at best.

Are you electrical saavy?
Positive Ground is no big deal.
Red is ground, Every other color is power.

1. Verify fuse is good, or at least there is one.
2. Verify continuity from ground post on battery to any suitable grounding location on frame.
No continuity, pull tank and seat and start chasing red ground wires.
There should be a connection of them at the 'Head Steady.' Sometimes these are burnt or improperly connected.

jsommer said:

J

• Modern Norton Motorcycles

76 Commando 850 basket case​

Hello, a friend inherited an 850 Commando from his dad that passed away. Knowing that I've worked on a lot of bikes. He asked me to put it together for him. I may have bitten off more than I can chew, this whole positive ground system has my brain completely twisted. His dad was in the middle of restoring it and to his knowledge, nothing was mechanically wrong with the bike. Had the tins painted, new tires. Etc. I thinking this was a slam dunk to putting it back together. I threw a new battery in, hit the key, and nothing, no lights, horn, starter or spark. Where should I start? Please don't tell me to get a manual, I have 2 for the bike and they are vague at best.

Click to expand...

What manual is vague?

Does it have a wiring diagram in it? There's nothing very vague about a wiring diagram.

A positive earth is nothing special unless someone has messed with the wiring.

Is the positive terminal on the battery connected to a red wire and is a red wire connected to the frame somewhere. Probably up by the head steady and also to a tag riveted to the inside of the headlight shell ?

The problem you face with people making suggestions is that after 48 years there is no telling what is there anymore. Which is why I suggest a wiring diagram and checking the most basic items like a red wire ground. The fuse as mentioned by Micheal is also a good start.

I'd suggest the first checks are to see if your wiring is still standard. People occasionally swap to negative earth but that's not common. What is very common is that people instal electronic ignition so much of the ignition wiring has gone. Also the old fashioned rectifiers are often replaced by a modern unit.

If you can establish your wiring is standard or close to standard and the earths are there I would check wiring to the main ignition switch. Old switches are often corroded inside and do not work. The fact nothing works probably points to a earth fail or the main switch failing or bad connections.

If you have a multimeter and can follow a wiring diagram I'd then go systematically step by step through the system.

Common failure points are the main and handlebar switches corroding.

Corrosion at the bullet connectors.

Poor spade connectors

Failure and poor connections at the horrible wire birdsnest under the tank common to all Commandos. Especially the five wire connector unit.

johnm said:

Especially the five wire connector unit.

Click to expand...

A '76 should make it a Mk3 which doesn't have the rubber five way connector.

L.A.B. said:

A '76 should make it a Mk3 which doesn't have the rubber five way connector.

Click to expand...

Excellent. A very good thing.

I'm more a Mk11 fellow. These sophisticated Mk111s are a bit much for us old blokes.

jsommer said:

J

• Modern Norton Motorcycles

76 Commando 850 basket case​

Hello, a friend inherited an 850 Commando from his dad that passed away. Knowing that I've worked on a lot of bikes. He asked me to put it together for him. I may have bitten off more than I can chew, this whole positive ground system has my brain completely twisted. His dad was in the middle of restoring it and to his knowledge, nothing was mechanically wrong with the bike. Had the tins painted, new tires. Etc. I thinking this was a slam dunk to putting it back together. I threw a new battery in, hit the key, and nothing, no lights, horn, starter or spark. Where should I start? Please don't tell me to get a manual, I have 2 for the bike and they are vague at best.

Click to expand...

Hi, welcome.


Please tell us more about your skillset, so we can be more expedient with remote troubleshooting.

Are you using the factory manual?

concours said:

Hi, welcome.


Please tell us more about your skillset, so we can be more expedient with remote troubleshooting.

Are you using the factory manual?

https://www.classicbike.biz/Norton/Repair/70up_Commando/70upCommando.pdf

Click to expand...

Unfortunately that manual does not cover his Mk111. There is no Mk111 wiring diagram in it.

Photos of the two page Mk111 wiring diagram frrm my Clymer manual.

Hopefully you can print them out or otherwise expand them.

Grant Tiller's MK3 enhanced wiring diagram.

Just to be clear. The diagram I posted is what you should find if it's unmolested.

Grant Tillers diagram is an ideal upgrade.

Grant's site has lots of harness variations including recommended changes for EI installs, but the one I posted is his correction of the manual wiring and follows what should be on a std MK3 with the exception of his deletion of unused wiring. All covered in his comments,

kommando said:

Grant's site has lots of harness variations including recommended changes for EI installs, but the one I posted is his correction of the manual wiring and follows what should be on a std MK3 with the exception of his deletion of unused wiring. All covered in his comments,

Click to expand...

One note on Grant's MK3 drawings. The blue wire between the two switch consoles is not always blue even though both blue is correct for most. This drawing shows how it was with standard switch consoles on the MK3 I recently rewired: https://granttiller.com/greg-marsh-mk3

Not a big deal but confused me a good bit as the console were the correct ones for a MK3.

While my sold off ‘72 was a 750 … I found it simpler to make up a harness from scratch , 25 yrs plus and afaik still running like a top ….

Craig said:

While my sold off ‘72 was a 750 … I found it simpler to make up a harness from scratch , 25 yrs plus and afaik still running like a top ….

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Agreed. Fixing harnesses, especially if changing to EI and/or Solid Stat regulator takes longer than making new and unless you check/change every connection you still probably have problems waiting to arise.

jsommer said:

J

• Modern Norton Motorcycles

76 Commando 850 basket case​

Hello, a friend inherited an 850 Commando from his dad that passed away. Knowing that I've worked on a lot of bikes. He asked me to put it together for him. I may have bitten off more than I can chew, this whole positive ground system has my brain completely twisted. His dad was in the middle of restoring it and to his knowledge, nothing was mechanically wrong with the bike. Had the tins painted, new tires. Etc. I thinking this was a slam dunk to putting it back together. I threw a new battery in, hit the key, and nothing, no lights, horn, starter or spark. Where should I start? Please don't tell me to get a manual, I have 2 for the bike and they are vague at best.

Click to expand...

It is possible you have connected the battery with negative to ground and positive to live. That would get you no power and likely smoke on a positive ground bike, assuming battery has a good charge. Red wires will be positive and connect battery positive to ground, likely more than one location on bike frame and engine.
If checking, replacing fuse, note if the glass type, likely it is rated with the old English system where say indicated 35 Amps means it will blow at that current and handles more like 17A continuous. A 35A SAE fuse is rated to handle up to 35A continuously, so likely cause problems for wiring in these bikes event of a short. Use a 17A SAE rated fuse as rough equivalent to 35A brit rated fuse.