Negative Ground Conversion

HELP!
I am considering converting my MKIII to negative ground make the starter turn backwards?

Mikeysduck said:

Will converting my MKIII to negative ground make the starter turn backwards?

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No.
As polarity is reversed in the field coils as well as the armature windings the starter motor continues to rotate in the same direction.

Thank You, for the quick reply. I have the wiring harness stripped apart. It is time to start putting it back together.

hello,
I'm in the process of converting to negative earth at the moment myself .
That's an inetreseting attachment to the front of the battery tray ? Is it the Horn ?
I'm putting my podtronics regulator there as it fits the air box mounting holes perfectly .
cheers

Also noticed you cut out the Z plates inner portion . I was thinking of doing that myself . Do you find it weakens the z plates a lot ?

1. Yes that is a horn. I could not find a stock, or repo horn at the time. I used a boat horn.
I've since added a Sparx 3 wire alternator. If you look closely you can see the Sparks rectifier / regulator is mounted. The tympanium is hanging down. I'm at a cross roads on the ground issue.
2. I haven't noticed any issue with the Z plates. However... I don't have any real miles on the bike. I cut the Z plates out with a round hacksaw blade. It took a while.

The bike's known history:
I have owned the bike since the 90's. I bought it seized, and thought no big deal. I didn't realize the PO ran it out of oil. Sufficient to say the internals, and cases were toast. I used a remanufactured cam.. MISTAKE. The first time It took me about 7 years to put it back together. Powder coated, stainless, new carb ignition... I put about 125 miles on it. The valves wouldn't hold an adjustment. The cam and followers were eaten alive. Metal everywhere inside the motor.

I took it to a shop. They went out of business, shortly after. It took me around 6 -7 years to find and recover most of my parts. The chassis was stored in a shed, in a mountain climate. My new chrome bits pitted. Careless handling tore a pipe off the isolastic hangers, and pulled a shock off its rubber mount... My new paint job chipped and scratched. The bike looked beat. When I got it home it was missing motor mounts, ignition and several smaller parts. The motor was re-assymbled but obviously had issues. The wrong nuts used on the cylinder base, stripped cylinder studs couldn't be torqued down. I was sickened and angry every time I looked at it. My polished jewel turned to crap. I stuffed it in my own shed for a few years while I collected parts. A second complete motor rebuild, new billet cam, new followers, new roller bearings reground journals, new pistons, better used rods. I started putting it back together about 30 months ago. Yea I'm slow. I get distracted with other moto interests.

There is not that much need to get it back on the road. I just have to motivate. I could get it done in two weeks if I applied myself. It's been sitting, as is, since about May.

Stick at Mickey ,looks like you have done all the hard work .
I have the problem in that my house renovations keep sucking my time . I dont have much to do on the bike either but time seems to fly . Mine was a non runner but is in good condition with only 7000 miles on it , and I could get it on the road in stock condition , ( did get it running ) but want to modernise the electrics and brakes for reliability and pleasant riding.
I have a late mk 3 assimilator module not the old type . This should in theory be capable of being made to work in negative ground . I will find out as soon as I get time . It a small flat module that sits under the stock airbox , so doesn't get in the way either.
It is summer down here and all these good riding days are going amiss !
cheers

The late MK3 assimilator will NOT work in a negative-ground wiring scheme. The diodes are all forward-biased and the transistors are in saturation. You may get the red charging lamp to turn on and off, but it will have nothing to do with the state of battery charging. There are suitable replacements available for negative ground; check the archives. Their logic is a bit different than the original assimilator, but they do respond to the state of the battery. Old Britts sells one, among others.

I have what I suspect will be a really dumb question, but please indulge me: I am genuinely curious. Why do people convert their bikes to negative ground in the first place? It strikes me that everything electrical is available for positive ground operation, which suggests that a conversion is unnecessary. I understand why you would want to convert from 6 volts to 12, but from positive to negative ground....? I know the rest of the world works on negative ground. Is that the sole reason to make the conversion?

ausnorton said:

Stick at Mickey ,looks like you have done all the hard work .
I have the problem in that my house renovations keep sucking my time . I dont have much to do on the bike either but time seems to fly . Mine was a non runner but is in good condition with only 7000 miles on it , and I could get it on the road in stock condition , ( did get it running ) but want to modernise the electrics and brakes for reliability and pleasant riding.
I have a late mk 3 assimilator module not the old type . This should in theory be capable of being made to work in negative ground . I will find out as soon as I get time . It a small flat module that sits under the stock airbox , so doesn't get in the way either.
It is summer down here and all these good riding days are going amiss !
cheers

Click to expand...

The late WLA would need simple mods to make it work neg ground. A second semester electronics tech/student should be able to do it. Swap the 2 diodes around, reverse + to - and the PNP transistor substituted for the equivalent NPN.
The original charging system would of course still need to be changed too.

My primary reason would be to run, off the shelf, cheap LED lamps. It's been years since I looked for these. You made me look again. I found some eBay. They are reasonably priced + ground lamps. I'll stick with the + ground.


http://www.ebay.com/itm/LED-stop-tail-b ... Qe&vxp=mtr

http://www.ebay.com/itm/12V-LED-stop-ta ... Ln&vxp=mtr

[quoThe late WLA would need simple mods to make it work neg ground. A second semester electronics tech/student should be able to do it. Swap the 2 diodes around, reverse + to - and the PNP transistor substituted for the equivalent NPN.
The original charging system would of course still need to be changed too.te][/quote]

Hello Dave ,
Looking at the wiring diagrams I can find of the assimiliator they show only a PNP transitor and resistors and no diodes .( I am eliminating the zeners and fittng a Podtronics regulator ).If you have a different diagram of the assimilator could you post it please ?
I would think if swapping the -ve and +ve around , and then running the other side of the indicator lamp to -ve ground it would work ( according to my diagram ). If not could the assimilator be taken apart to do it your way ? By the way its been about 20 years since I messed with electronics so I have forgotten more than I remember ! :shock:
Cheers

Can someone tell me the benefit of changing to -ve earth. I've been an aviation electrician for 40 years and cannot see the point. I run a 200W single phase alternator, gel battery, AWG6 Mil Spec starter wires, have no reliability issues and always start on the button.

There is a lot of conjecture as to the reason for +ve versus -ve earth systems . This all stems from the 40's and 50 's where the insulation materials of wiring and hardware was not the best and would cause corrosion of terminals and frame . This depends of course on who you believe whether -ve or +ve was better. However from the mid 60's on and with the use of modern plastics and insulation there really is no difference . It was more the use of electronic components and the standarisation of -ve earth in equipment that made +ve earth obsolete .
Any electronic items you may want to use , such as electronic gauges and GPS will probably have their frames grounded -ve .( Trispark and Podtronics can work with both ).
Of course it would be not desirable if -ve and +ve earths were in use together just in case :idea: . If you are keeping your bike stock then it doesn't matter what system you run , only modified bikes need be wary .
I also just like to keep with convention .

ausnorton said:

There is a lot of conjecture as to the reason for +ve versus -ve earth systems . This all stems from the 40's and 50 's where the insulation materials of wiring and hardware was not the best and would cause corrosion of terminals and frame . .

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If you leave a bare (acid type) battery just sitting, observe which terminal will corrode over first.....

There is also the minor matter that the early selenium rectifiers only came in a +ve earth variety,
and it has been suggested this is why the Brit motor industry moved to +ve earth vehicles.

But what did the american auto industry do for rectifiers then ??

On crimping vs soldering -

The OEM soldered bullet connectors on my Commando are only soldered at the very tip where the wire pokes through the end and the loose wire on the inside has very little room to vibrate and bend, so it doesn't fail at the solder joint.

Yes, production efficiencies could explain the universality of crimping in the automotive field but I think not in aviation and aerospace where reliability trumps cost savings.

I'm no electrical engineer but all I see is that all marine, aviation, automotive, and motorcycle applications are crimped. Indeed, except for circuit boards, consumer electronic sub-component connecters are crimped too.

That said, I do solder some joints. When I have to repair a run of wire with a butt connection, and if I do not anticipate any need for a future disconnection, I do solder and shrink wrap it, BUT before shrink wrapping, I slip a splint under the shrink wrap. I save the cut off tag ends of nylon zip ties for that job; they slip in easily and are stiff enough, to splint the joint. If the shrink and the splint go well beyond the joint, then a vibration break is unlikely.

Mr.Sparks said:

Can someone tell me the benefit of changing to -ve earth. I've been an aviation electrician for 40 years and cannot see the point. I run a 200W single phase alternator, gel battery, AWG6 Mil Spec starter wires, have no reliability issues and always start on the button.

Click to expand...

No benefit so far as I know other than much better compatibility with modern accessories like LED lights, chargers, etc. I suspect the positive ground convention was a carryover from telegraph and telephone systems where it really does make a big difference when conductors literally contact the earth/ground, telephone systems are still 48V positive ground in NA to this day. No such advantage on a vehicle but I've resisted converting my Commando to negative ground just because. Anyway FWIW there is much more on why positive ground is the standard for telephone/telegraph systems at
http://lyle.smu.edu/~levine/ee8320/positiveground.pdf

bluto said:

I suspect the positive ground convention was a carryover from telegraph and telephone systems

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+ve earth only appeared on british cars/bikes in the early 1950s, prior to that they had pretty much all been negative earth.

It has been suggested that +ve earth appeared in preparation for the adoption of alternator electrics - and all the early selenium rectifiers were +ve earth,
hence the stampede in that direction....

??

Or they did it just to be contrarian--though that sounds more French than British

Hi to all.
Ok so I am ignorant but I cannot see what the benefits are that you will get out of changing from positive earth to negative, a load of hassle and expense maybe ?. I have a 1972 Mk3 750 which functions perfectly well on its original set up so why change if it aint broke.