The difference between Positive and Negative ground

The more I look at the wiring on my Norton the less it makes sense, none of it is standard and I'm reasonably sure there are white 'earth' wires connecting to the negative battery terminal. Is there a simple way to tell if the previous owner converted it to negative ground?

A very tricky - and important - question, if the wiring is non-standard.
It should be mandatory to put a sticker somewhere prominent if its now -ve earth.
And include a modded wiring diagram printed on paper with any sale.

You don't say which year/model of Commando, makes a (slight) difference

Only the zener and an electronic ignition, and the blue can are fussy about polarity, all the rest is non-specific.
An ammeter on an early model probably needs to be included in the fussy list.

Have a look at the zener diode, down on the right side z footrest plate.
Is there still a red wire connected to it, and is it still connected (ultimately) to the +ve on the battery.
If its been converted to -ve earth, the zener usually needs to be disconnected/removed.
It may need quite a careful look at the wiring, to see what has been done to it...

Or you could wire it all up to the battery +ve earth, and see if any smoke comes out !!
Have fun....

P.S. Is an electronic ignition fitted to this bike ?

Examining that, and seeing if it is a +ve or -ve earth variety would probably be a good first step.
You may only get that by examining the model number, and studying its specs online....

Using a multi meter you can measure directly from either terminal of the battery to earth (frame , head , z plate) if you set the MM to say 20V DC, if you measure from the positive (+)terminal pn the battery to the earths (grounds ) as mentioned and get no reading ) 0 volts it will be positive earth, if you measure from the negative terminal and get 12 + Volts it will be positive earth. Opposite for negative earth ! Hope this make senxse
Regards Mike

Perhaps we should have asked first is a battery currently fitted to it, and the bike is running ?

Branch said:

The more I look at the wiring on my Norton the less it makes sense, none of it is standard and I'm reasonably sure there are white 'earth' wires connecting to the negative battery terminal. Is there a simple way to tell if the previous owner converted it to negative ground?

Click to expand...

Well, if it does turn out to be negative earth/ground, then we need to go back to square one again at: boyer-tri-spark-conversion-progress-t21783.html and start from scratch, and hope that connecting the Tri-Spark for the wrong polarity hasn't damaged the ignition. :?

In response to your thread title: "The difference between Positive and Negative ground", there is no practical difference but you MUST choose either positive OR negative.
Multimeters are cheap: get tracking those wires and sketch them out for us.

L.A.B. said:

Branch said:

The more I look at the wiring on my Norton the less it makes sense, none of it is standard and I'm reasonably sure there are white 'earth' wires connecting to the negative battery terminal. Is there a simple way to tell if the previous owner converted it to negative ground?

Click to expand...

Well, if it does turn out to be negative earth/ground, then we need to go back to square one again at: boyer-tri-spark-conversion-progress-t21783.html and start from scratch, and hope that connecting the Tri-Spark for the wrong polarity hasn't damaged the ignition. :?

Click to expand...

This is exactly my concern! I don't mind buying another Tri Spark if needs be as I think it will be worth it in the long run, it just got me thinking about my issue with the reversed wiring. I'm reading up on this as much as I can but it's a tough subject to wrap my head around. Matt from CNW (who I bought the Tri Spark from) supplies very useful diagrams for connecting the Tri Spark on both negative and positive earth Commandos so I can switch it over if needs be, it does involved cutting into the wiring on the Tri Spark though so I'm reticent to do it unless I know for sure either way.

needing said:

In response to your thread title: "The difference between Positive and Negative ground", there is no practical difference but you MUST choose either positive OR negative.
Multimeters are cheap: get tracking those wires and sketch them out for us.

Click to expand...

I bought a multimeter just last week, although I am slightly intimidated by all the symbols on the dial! If my grade school understanding is correct, on a positive earth Commando the power would come out of the negative battery terminal, flow through the circuit and then go back via the positive terminal - is this correct? If so then I would assume the opposite configuration would be negative ground?

Rohan said:

P.S. Is an electronic ignition fitted to this bike ?

Examining that, and seeing if it is a +ve or -ve earth variety would probably be a good first step.
You may only get that by examining the model number, and studying its specs online....

Click to expand...

Hey Rohan, there was a Boyer fitted and I'm now in the process of fitting a Tri Spark. The Tri Spark LED only lights up correctly when I reverse the wires leading to it, which has been baffling me for a while and I can't get it to start at all - although the sparks both work.

Brooking 850 said:

Using a multi meter you can measure directly from either terminal of the battery to earth (frame , head , z plate) if you set the MM to say 20V DC, if you measure from the positive (+)terminal pn the battery to the earths (grounds ) as mentioned and get no reading ) 0 volts it will be positive earth, if you measure from the negative terminal and get 12 + Volts it will be positive earth. Opposite for negative earth ! Hope this make senxse
Regards Mike

Click to expand...

Hi Mike, I'll do this today and update with the results.

I was lucky on mine even tho there wasn't a battery in it when I bought it.

The previous owner marked the wires. I still took the time to verify that it had been converted to negative ground as the wire marking indicated.

Even with the old wires you should be able to figure it out pretty easily. Set your VOM to ohms and check each battery wire (disconnected from the battery) to ground. If you read resistance that's the ground side. You can trace other wires in the circuit the same way.

You also can trace the wires back and see which one(s) are earthed...bolted to the frame or engine.

If the color coding is messed up it makes it a bit more difficult. Mark them as you go.

Edit: Some resistance in the wiring might be read on the hot side so I usually set the VOM to the lowest setting (200 ohms)...it will usually flop over to no reading and show a little flashing ohm icon on the screen with a grounded wire which is what you are looking for. Touch the VOM probes together once you set it and see what your meter does.

Okay I figured it out, the entire wiring loom is non-standard and I've been finding it very confusing as it doesn't seem to match any wiring diagrams I've seen for the Commando. It's a positively earthed bike after all, but thanks for the comments here as they taught me quite a lot!