conversion to negatigve earth.

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Deets55 said:
Excellent point, gotta love that LED technology. Now if we can just get the bulb builders to convert to positive ground HUMM.......

Pete
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CNW sells a very nice LED tail light module that works perfectly with my positive ground 72 Combat.
:mrgreen:
 
PeterJoe said:
There are only 4 electrical items on a 1974 Commando that are polarity sensitive:

  • 1. Zener Diode (voltage regulator)
    2. Rectifier (the alternators AC to DC converter)
    3. 2MC Capacitor (used for running without a battery)
    4. Spark Coils

To convert to a negative ground is pretty straightforward:

  • 1. You will need to replace the Zener Diode to one with a negative ground.
    2. You need to replace the rectifier with an aftermarket bridge rectifier which you would need to wire negative ground
    3. Swap the wires on the 2MC capacitor. They have different sized terminals so those would have to be changed.
    4. Swap the primary wires on the spark coil
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This list makes it seem easy enough to do. I have a couple of dumb questions, though ...
I would like to do this on my 850 Mk3 - is there anything else to consider besides the starter (which in my case is a non-issue since I've disconnected it)?
Also, no one has mentioned the battery terminal connections. I would guess they need to be swapped, no?

Thanks in advance!
 
To convert to a negative ground is pretty straightforward:
1. You will need to replace the Zener Diode to one with a negative ground.
2. You need to replace the rectifier with an aftermarket bridge rectifier which you would need to wire negative ground
3. Swap the wires on the 2MC capacitor. They have different sized terminals so those would have to be changed.
4. Swap the primary wires on the spark coil
Click to expand...

And don't forget to put the battery the right way around.

I kid you not I was left stranded miles from home with a dead battery.

I had just bought the bike and the previous owner decided to put in a solid state regulator.
That was fine except it was a dedicated negative earth one ,only had 2x yellow A/C wires and one red one +ve DC and the earth was via the case.
HOWEVER and I repeat HOWEVER he never swapped the earth point on the battery ( or kept putting the battery in without thinking) so the battery was +ve earth and the regulator was -ve earth.
One can only imagine the electronic confusion going on.
The bike ran long enough to get me 50 klms from home before it stopped.

Once I figured out what was happening and that took some head scratching on the side of the road (who expects a curve ball like that) I simply physically turned the battery around so the batt -ve was now earth, bump started and rode home.

I suspect the reason he sold me the bike is it would always strand him with a flat battery all the time .
Oh and the fact he bodged up the cracked RH4 head, but that's another story

So add to the list to ensure the -ve battery terminal is now the earth.

Peter R
 
That's the reassurance I was looking for. Maybe it was just too obvious to list.

Thanks!
 
After my debacle with the PO installation and when I finally sorted everything out I put in a new battery.
I use a battery where the terminals can be on either side of the battery, the lugs are screw fitted to the battery and the battery is universal with 2 mounting points for + and 2 for - , or ensure the terminals are on the correct side before purchase a new battery.
When you go -ve earth you have to mount the battery the other way around , at least that's what I did and now the wiring has to go to the far side of the battery and there maybe a length issue (although I'm told size doesn't matter).

Food for thought

I also put a length of black heat shrink over the red wires on the battery terminals just to remind me that is now negative earth.
It's a seniors thing, you know what I mean !!
I have enough trouble remembering 1 up 3 down when going from bike to bike, let alone sometimes the brake is where the gear change should be.

Cheers
Peter R
 
Yup senior here as well. For now I am leaving the bike posi earth. I fitted 2 Led spots and aimed them out and up slightly. I can now see the road going round bends etc. As there is no park [ pilot ] light, the park/head light switch has been used to switch on the spots, and they only come on in high beam. Main beams operate direct from relays. [ had to fit another relay for the spots. Its amazing how much crap you can fit into the headlamp nacelle ]
Was a bit of a fiddle mounting the brackets for the spots and my first mistake was to mount them too low so the light reflected in my indicators. Have now added another bracket to each side. All nicely shaped and painted matt black. I like it.
Have ordered spare chains from Andy as well. Out with the Tsubaki.
Dereck
New mufflers arrived for the 750 this week as well. Leanometer [ accountant/wife ] still happy .
 
searunner said:
probably for Modern LED HeadLight -conversion to negative earth are unnecessary -
they aren't sensible to pole, and can be mounted with Negative and Positive GROUND
I have just ordered one and waiting the arrival (for My Commando Roadster 74 POSITIVE Ground) and then I can confirm - my viewpoint
http://www.ebay.it/itm/8-16V-H4-High-Lo ... 2590bf4188
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'Same here; I noticed a number of these are listed as "Toyota compatible", so there's something going on here that probably has to do with their computer recognizing a blown bulb (fused globe?). Whatever it's called, as long as we benefit from it! http://www.ebay.com/itm/111352030430?_t ... EBIDX%3AIT
I'm also waiting for these to arrive. http://www.ebay.com/itm/171378073381?_t ... EBIDX%3AIT I'll affix one below the headlight, wired to the pilot light circuit. Pictures to follow once they show up! The waiting is the hardest part, Tom.

Nathan
 
contours said:
This list makes it seem easy enough to do. I have a couple of dumb questions, though ...
I would like to do this on my 850 Mk3 - is there anything else to consider besides the starter (which in my case is a non-issue since I've disconnected it)?
Click to expand...

There are a couple of things that I can think of that are different on the Mark III than the earlier Commandos.
1. The Mark III has 2 zener diodes that act both as part of the rectifier and voltage regulation. Also the rectifier has only 2 diodes in it instead of 4. I would think changing those components out in favor of an aftermarket voltage regulator would be the easiest way to go to convert a motorcycle to negative ground.

2. The warning light assimilator has electronic components so it is polarity sensitive and would also need to be replaced. There are a number of different companies that have warning light assimilaters that would work with a negative ground system. I just saw this unit and thought it was kind of neat because it has more features than simply saying that the alternator is working. http://www.improvingclassicmotorcycles.com/products.htm They come in both positive and negative ground.

contours said:
Also, no one has mentioned the battery terminal connections. I would guess they need to be swapped, no?
Click to expand...

I was wondering when somebody was going to notice that I forgot to mention swapping the battery leads. In my mind it was so obvious that I forgot to mention it. Good catch!

Additional information if you ever plan on using your starter motor. Starter motors are not polarity sensitive however on the starter relay there is a white/purple wire that acts as a ballast resistor bypass and goes to the spark coils. The white/purple wires need to go to the spark coils positive terminals along with the wire from the ballast resistor and the wires from the points/condensers go to the negative terminals of the spark coils. This would apply to your motorcycle if it is still using the points type ignition system. If you have an electronic ignition system then you would wire it in accordance with the manufacturer's instructions and the white/purple wire should be disconnected at the starter relay.
 
[I was wondering when somebody was going to notice that I forgot to mention swapping the battery leads. In my mind it was so obvious that I forgot to mention it. Good catch! /quote]

I know what you mean, but I got caught out by a previous owners folly.
From may years of putting together lists and procedures you think you have covered every possible situation but there is always someone that finds a new and novel way to do it wrong.
I remember a clip where someone put an electric drill bit through his nose and when asked he said it never said don't scratch you nose with the drill bit.

I coined a phrase " You can never make it idiot proof the best you can do is make it idiot resistant"
I'll stop now before being told to go to the naughty corner again.
Click to expand...
 
bluemax said:
I remember a clip where someone put an electric drill bit through his nose and when asked he said it never said don't scratch you nose with the drill bit.
Click to expand...

That is stinkin' hilarious!!
 
Another great thread, I'm considering making a custom wiring loom for my MK2 and had thought of converting to neg earth since I'll be replacing almost all of the electrical gear on the bike.
 
Rohan said:
What is a 1984 Commando ?
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when you think back ~ 40 years to when you last owned and rode a commando, doesn''t take much then to be off ..ooh, a decade or so,

my username should have been 74ok
 
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