Negative Ground Conversion on my Commando Mk3

When I rebuilt my Mk3 two years ago I upgraded the electronics and built a new harness, but stayed with the original positive earth grounding scheme. Last year I bought a new bike, and added the usual stuff that makes for comfortable riding in the off-seasons, like heated gear and GPS. Wouldn't it be great, I reasoned, if I could import all that stuff over to the Commando? I would use it more frequently in the winter, and wouldn't get lost as much. Clearly, a negative ground conversion was needed; here's how I did it:

Priliminary -

1. The Zener regulator has got to go, and be replaced by a solid-state rectifier/regulator. If you're wedded to the Zener, read no further; the Zener is positive ground only. A new device is less than 50 bucks, although this would be the time to upgrade to a 3-phase alternator as well.

2. The solid-state OEM assimilator on the Mk3 is also hopelessly positive ground. Negative ground replacements exists that do a similar, although not duplicate job. I bought mine from Old Britts; this unit measures the alternator voltage and compares it to an internal voltage reference set at 12v. When the peak alternator voltage exceeds 12v (8.5 vrms) the warning light circuit opens and the light extinguishes. This unit DOES NOT SEE the battery voltage.

Now the Work -

3. Disconnect and remove the battery. Remove the master fuse. Remove the left side panel and fuel tank. Remove the carburettor air filter.

4. Remove the OEM assimilator and install the new negative ground assimilator. Attach the existing ground wire to "E", and the white/black wire from the warning light to "WL". Attach one of the two alternator wires to "AL" and snub-off the other. Snub-off the unused white ignition wire as well.

5. I'm using a SPARX reg/rec, but the others are pretty much the same, with floating outputs. Swap the destinations of the red and black wires coming out of the device. The red wire will now be going to the new +12v point, either a fused connection or directly to a brown/blue wire. The black wire will now go directly to a chassis ground point, where it will join several red ground wires from the original wiring.

6. Coming out of the Pazon module, disconnect the white and red wires from their destinations. Connect the white wire to ground, and the red wire to switched +12v (this could be the white/yellow wire coming from the kill switch). Leave all other connections intact. All EI suppliers provide schematics and instructions concerning negative ground installation.

7. Regarding after-market relays, some of them will work with either polarity at the coil, some won't. Rather than test each one, simply swap the wires at each coil connection for each relay. Done!

8. Leave the starting motor circuit alone! The motor solenoid works with either polarity, and the rotation of the motor itself only depends on the winding geometry, not on the polarity.

9. That's it. You're done. Replace the battery, remembering that your brown-blue cable will now attach to the POSITIVE terminal, and your primary ground point will now connect to the NEGATIVE terminal. Check your work again, then install the master fuse.

10. Replace the fuel tank (blip the throttle a few times to insure there are no kinks in the cable) and air filter. Revise your schematic and place a label near the battery stating "This Norton has been wired for NEGATIVE ground". Replace the side panel.

11. Turn the ignition switch, observe the warning light glowing red, press the magic green button (or alternatively give the bike a good boot) and hear it spring to life. This process took me an afternoon, and I'm a very cautious guy.

-ve Ground Zeners were made for Triumph when they went -ve earth, may have been the same time they fitted the Rita ignition. I fitted one to my Commando when I went -ve earth to fit an alarm, its was 3 zeners on a block of aluminium and each zener was connected to a phase of the 3 phase alternator I fitted at the same time. The alarm went wonky in the wet and did not last long.

Cleaver but bit risky for future owner what with red wires to chassis being retained.
What do ya do about the blue can polarity, if it matters d/t its construction?
I too want GPS and heated stuff and radar detectors on my special so wiring up up from scratch again. All the automotive relays I've gotten off the shelf didn't care which polarity used to switch em. There are cute 1/2 size ones too.

Steve,

The confusion over the red wires is what kept me from making this conversion earlier. When I created the harness, I used the original color codes on all wires, so RED ment, unambiguously, GROUND. Black was rarely used in the original harness, so I guess I could pull out all of the original red ground wires and replace them with black. I could keep the Brown-Blue "hot" wire convention and have it live alongside the new red +12v convention.

My primary ground point (there are three, connected by a heavy RED ground wire) is shown below.



You can see the lonesome black wire in a nest of red.

Changing out the ground wires would be a multi-day task; inside the headlamp shell is a sea of red. January??

I got rid of the blue can when I rebuilt the bike and installed EI. It does pose a problem, as it is an electrolytic and must maintain its original polarity with a positive case ground. Looks like collateral damage that comes with the conversion. Do you really need it?

Rick

Ugh I could not bring myself to undo harness to change red earths. I'd just make sure I remembered and told mechanic or new owner how it is and enjoy riding with a nice big robust earth connection : ) If blue can unneeded for EI then more power to ya. I have had to run home after a battery flung out and think the can allowed me to get a tow start and run home on analog Boyer. It the alternator phase of voltage pulse coincided with the coil triggering likely wouldn't need battery or blue can.

The red earth wires rubs me the wrong way too, but I deal with it. Being able to use standard LED lamp assemblies is a wonderful thing.

Word of warning though - even the highest output alternators for our bikes is only 200 watts or so. Heated clothing is not in the cards.

maylar said:

The red earth wires rubs me the wrong way too, but I deal with it. Being able to use standard LED lamp assemblies is a wonderful thing.

Word of warning though - even the highest output alternators for our bikes is only 200 watts or so. Heated clothing is not in the cards.

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I will be fixing that problem, I'm fitting a denso 400W alternator. It won't fit in the stock location, it's custom install. It's been done before.

400 watt is sure nice power increase. Is it your rig that drives the DENSO via thin belt behind the crank belt pulley? I stared at that set up a long time. Best I could find for Peel was ebay snagging a pair of 600 watt'rs. I need to keep belt drive enclosed d/t THE Grit so would have to slit the inner cover to fit the Altn. belt but figure I could strap across the case slits to get its support back and protect from fracture on the loads it carries in Peel, outter rigger bearing and blower impeller drive and alignment. I mean if we come inside every time it rains or gets below freezing we sure miss out on a lot of life on our obsolete wonders.

Steve,

I had always thought that gentlemen never motor in the dark or in the rain.

Maylar,

SPARX claims 200+ watts max on my 3-phase alternator system, as you ponted out. I figure 70 watts for lighting, 18 watts for EI, 60 watts for my electric vest, another 40 watts max for the intermittent stuff (indicator lights, brake lights), I should still be under 200 watts. I'm fully fused for 20 amps of regulator current. Maybe I'm missing something. I haven't tried the vest yet, so I can't speak from experience.

Rick

Steve,

My reservations over the blue can capacitor were not well-founded. I checked the one in my parts bin, a replacement 700 microfarad cap that came attached to the spring holder of my Mk3, and the two leads float with respect to the case. If this is true for the original blue 2MC capacitor, then there is no problem keeping it in the circuit, just switch the leads so that the positive tab goes to +12v. Check first for electrical isolation from each tab to case.

Rick

Rick I'm no gentleman when on a motorcycle when in raw wild road life. 80-85 is my most comfortable speed after dusk not because I like that speed after dark but because my groin grabs the least knowing a deer can't strike me from the side just T-boned I may have change to survive or die before I know what hit me and ride around the next run for ever and ever more.

Condenser/caps should act like little battery and be wired the same, glad Norton kind don't care the polarity.

Wife just read this and said smiling I'm a heathen all the time, but hey you know how women see things. Off with my Cdo buddy Wes to see if we can find Tron movie in town.

rick in seattle said:

Steve,

I had always thought that gentlemen never motor in the dark or in the rain.

Maylar,

SPARX claims 200+ watts max on my 3-phase alternator system, as you ponted out. I figure 70 watts for lighting, 18 watts for EI, 60 watts for my electric vest, another 40 watts max for the intermittent stuff (indicator lights, brake lights), I should still be under 200 watts. I'm fully fused for 20 amps of regulator current. Maybe I'm missing something. I haven't tried the vest yet, so I can't speak from experience.

Rick

Click to expand...

I have the Sparx 3 phase and I like it a lot. But at idle the battery still does it all. You don't get that 200 watts under 3000 rpm.

Though you can gain back quite a bit with LED blinkers (std bulbs are 21 watts each).

Great write up and instructions. I have a Pazon already and had Positive Earth ground. I just switched to a Podtronics and followed your instructions to switch to Neg Earth. Worked great. Of course with every connection to the battery and then turning the switch, was with a bit of trepidation. One change I had to do was swap the polarity of the Blinker control I have and also the polarity of the multi color LED voltage monitor. All else is right on the money. Now when I get my bracket for the new electronic speedo/tach, I can hook that up and know the blinkers etc should be fine. Thanks for taking the time to make this 'how-to'.

About 18 years ago I did a complete rebuilding of a 74 barn saved.. Boyer, Podtronics, and neg ground. Electrics are not my strong point. Sometimes my mind would just lock up like a drum brake in the rain. I studied the original wiring diagram and the instructions that came with the new components, made changes to accomodate the different components, and then drew my own diagram. I put a terminal block under the seat, and ran pretty much everything to and from it. This worked well.

I sent that last post in error. I wasn't finished. I have now started a rebuild of the 73 that I bought new from Del's Cycle Center in Schofield, WI USA in the spring of 74. I quit driving it 13 years ago due to my inability to kick it with bad knees, so I went Japanese. Now I see an electric start available that looks like it will hold up (CNW). This one will get a 3 phase stator, electonic regulator, Boyer (I have some left over), Dyna twin lead coil, and all LED lights. I solder and shrink tape all connections. I have done some Iron Butt challenges and want to go in the book with a Norton. Good luck with your rewiring. I would rip it all out and start over. But that's just me.

Never solder any connections that are subject to vibration. Crimp only. You'll never see a soldered connection on any vehicle from a manufacture unless it is potted. Many a Boyer has failed due to fractures at the solder connection of the pickup leads.

JimC said:

Never solder any connections that are subject to vibration. Crimp only. You'll never see a soldered connection on any vehicle from a manufacture unless it is potted. Many a Boyer has failed due to fractures at the solder connection of the pickup leads.

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Or, better yet, both can be done... even with the el-cheapo auto store connectors. Just pull off the hard plastic sheathing, crimp the wire, then solder the joint. Finish with some shrink tube.

No solder. The solder wicks up the wire, turning it into solid core for a short distance. Solid core wire will fracture when subjected to vibration. The insulation will remain intact, but the conductor will separate, making it impossible to find visually. That's why you never see soldered joints on a vehicle when it leaves the manufacture. Do not solder connections on your Norton or anything that vibrates.

Crimp and then solder with heat shrink is fine if done right. You solder just past the crimp (where the end of the wire is) and don't heat the piss out of it so the solder doesn't wick all the way up the wire. I use the "high voltage" thicker heat shrink which contains hot glue. Mouser.com. The heat shrink does all the strain relieving. With the black heat shrink it also looks a lot better than a blue or red or pink piece of plastic. Don't like seeing those on anything.

If you have a proper crimp, solder is totally unnecessary and only introduces a probable failure.