Just want to make sure I don’t mess something up.

KNorton

KNorton

Joined
Jan 9, 2020
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Just bought a 1971 Commando. I’m aware they are positive ground but does that simply mean to install the battery “backwards”? Red cable to black terminal and black cable to red terminal? Sorry, the bike didn’t come with a battery.
 
concours said:
Red cable to the "+" terminal on the battery, brown/blue to the "-" terminal on the battery.
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The Wire with the fuse in it, goes to the Negative, If the MC has the original fuse holder with the "glass fuse" in it . The OEM fuse was a special fuse, but is hard to find, so I use a 20 amp fuse, some people use lower amp numbers. 10- 15 amp.
 
Carl H said:
The Wire with the fuse in it, goes to the Negative, If the MC has the original fuse holder with the "glass fuse" in it . The OEM fuse was a special fuse, but is hard to find, so I use a 20 amp fuse, some people use lower amp numbers. 10- 15 amp.
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Yes the brit standard fuse rating are different...the indicated rating is the is the immediate blow amperage, while a US rating is the max operating rating. So fitting a 30 A US spec fuse to replace the 30 A UK fuse will mean no blow at 30 A...which could melt stuff. I use a 15 A US spec fuse on my Commando without problems.
 
I’m confused now. How does it ground through the positive terminal if I connect it correctly? I’m a complete noob here. Somebody teach me something.
 
KNorton said:
I’m confused now. How does it ground through the positive terminal if I connect it correctly? I’m a complete noob here. Somebody teach me something.
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It is just that the ground is now from the positive batt terminal instead of the negative terminal. The frame/engine block etc is now positive instead of negative. Electrons "flow" the opposite way around the bike back to battery, but no need to worry about that level of detail. Just habe red wire to battery positive...and follow where they end up, which should to the engine head steady plates or sometimes other frame positions. Negative wire goes to a fuse on original wiring, then off to other components like the regulator and ignition switch.
 
Thank you! I’ll probably have a million questions later about how to convert to negative ground. My brain just can’t wrap around a positive ground. It just seems to go against everything I’ve ever been taught!
 
KNorton said:
Thank you! I’ll probably have a million questions later about how to convert to negative ground. My brain just can’t wrap around a positive ground. It just seems to go against everything I’ve ever been taught!
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Welcome to Brit Bike World. You will also have to get used to shifting on the right. Seriously, any new Norton is likely to have a whole pile of problems, from elderly tires (easily fixed) to low compression (not so easily fixed). Just connect up your new battery and worry about converting to negative ground later.
 
Yes, I too was new to positive earth setup when getting ny Commando 9 yrsago...have not converted to neg earth yet...there is very little reason too...even LED lighting is now generally available to positive earth or, better yet, polarity-insensitive LEDs (swings both ways :D!). Only some more advanced things like turn signal cancel or brake light flashers need negative ground.
 
That’s really the only thing I was worried about. So what do I do if the headlight or brake light (no turn signals….yet) burn out?
 
KNorton said:
That’s really the only thing I was worried about. So what do I do if the headlight or brake light (no turn signals….yet) burn out?
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Well nothing if they are original incandescent types...they are all available in the original bulb formats from suppliers like Andover Norton, RGM, Paul Goff, Greg Marsh (in the USA), Classic Bike Spares (CBS) etc. if you want better lighting, like for the headlight main bulb, then a new reflector with correct bulb socket can be used, but I have used an adaptor ring to put an H4 type bulb in the original British PreFocus reflector socket on my classic Mini headlights. There are also LED headlight bulbs that are direct fit to the Brit PreFocus socket. The brake lamp is just the normal everyday two filament socket...same for turns (but single filament).

Also, never forget the immortal words of Joeseph Lucas...A gentlemen never rides his machine at night.
 
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Negative ground
Power runs from positive to negative
Think of it as left to right


Positive ground
Power runs from negative to positive.
Think of it as right to left.

Power just reverses itself.
Battery doesn’t care.
 
KNorton said:
Thank you! I’ll probably have a million questions later about how to convert to negative ground. My brain just can’t wrap around a positive ground. It just seems to go against everything I’ve ever been taught!
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Way simpler to just understand that + is ground. While you can find drawings showing the bike wired as negative ground, all official manuals will be positive ground.

This was not that abnormal in the 50s/60s even though most US and German car manufacturers had switched to negative ground during the 50s but Volkswagen was in the 60s. Most British cars switched by 1968. The switch often happened when going from 6-volt to 12-volt systems and alternators rather than generators. I understand if you're young, but us old guys had US cars with positive ground and then the next might be negative ground or vice versa.

If you insist on going to negative ground, then get friendly with this site: https://granttiller.com/ At least his drawings can be trusted. I understand British bike wiring fully, and I never switch to negative ground even though it would be easy for me - they next guy to own the bike would be lost.

And PLEASE, if you switch to negative ground, switch the ground wires from red to black! The other wires can remain. For instance, white is "hot" and used for the ignition - that can remain without a lot of confusion but if you leave red as ground in a negative ground system, you better learn to do it on your own because direct help will be hard to find and people will keep getting confused here.
 
marshg246 said:
Way simpler to just understand that + is ground. While you can find drawings showing the bike wired as negative ground, all official manuals will be positive ground.

This was not that abnormal in the 50s/60s even though most US and German car manufacturers had switched to negative ground during the 50s but Volkswagen was in the 60s. Most British cars switched by 1968. The switch often happened when going from 6-volt to 12-volt systems and alternators rather than generators. I understand if you're young, but us old guys had US cars with positive ground and then the next might be negative ground or vice versa.

If you insist on going to negative ground, then get friendly with this site: https://granttiller.com/ At least his drawings can be trusted. I understand British bike wiring fully, and I never switch to negative ground even though it would be easy for me - they next guy to own the bike would be lost.

And PLEASE, if you switch to negative ground, switch the ground wires from red to black! The other wires can remain. For instance, white is "hot" and used for the ignition - that can remain without a lot of confusion but if you leave red as ground in a negative ground system, you better learn to do it on your own because direct help will be hard to find and people will keep getting confused here.
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Over on Frank DelMonte's U-tube channel a few videos ago he was discussion positive or negative earth bikes. He basically stated he will refuse to work on a Commando in his shop if it has been converted to negative earth, basically b/c he's getting too long in the tooth to make his brain work out how things work different. A bit extreme I guess, but to each their own...
 
Tornado said:
Over on Frank DelMonte's U-tube channel a few videos ago he was discussion positive or negative earth bikes. He basically stated he will refuse to work on a Commando in his shop if it has been converted to negative earth, basically b/c he's getting too long in the tooth to make his brain work out how things work different. A bit extreme I guess, but to each their own...
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I will work on them, but I no long fix wiring. Fix one thing and the customer is back with another with 50+ year old wiring. I will completely re-wire and in negative ground if pushed but I prefer to stay normal which is positive ground.
 
KNorton said:
Thank you! I’ll probably have a million questions later about how to convert to negative ground. My brain just can’t wrap around a positive ground. It just seems to go against everything I’ve ever been taught!
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If you don't have a means of testing continuity you need one, as Greg notes, you are working with old wiring with corrosion issues.

And you need to use your tester, volt/ohm meter, whatever. Check where the red wire goes, even just physically if you don't have one.

Your bike will work positive ground. Just as it worked for all of the time before you bought it. Why change it?

You are probably going to have other more important things to do. Why make work?
 
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Ok, so basically there is no need to convert anything except my brain to positive ground. I was thinking the light bulbs were polarized and if wired backwards they would blow. I guess not. So I guess I’ll leave well enough alone. It’s worked fine for this long so why change it?!?!
 
I changed mine to negative earth decades ago as I wanted to fit an alarm that was earthed through its body. After a few years when the alarm failed I quickly changed it back so I could use the manual wiring diagram instead of trying to remember what I had or had not changed when by the side of the road on a dark night.
 
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