Boyer ignition converting to negative ground

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May 4, 2005
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Has anyone converted their bike to negative ground? and will converting my current Boyer to run require me to just simply reverse the wiring( on the coils and the Boyer unit) or does the internal electronics require the positive ground setup. Any advice would be appreciated. My current unit is analog, I assume with the digital it would not be possible.

I have purchased a 3 phase Tympanion reg/ rectifier and it requires neg ground. I figure this gives me the opertunity to convert the bike, with neg ground. I would get more flexability and choices as fas as modern electronics, LED bulbs, etc.
Thanks for the link Captain. I guess that answers my question of whether the Boyer can be converted to neg ground.
Norton Fans,
Anybody had any issues converting to Neg Gnd? I followed the instructions from BritCycle last night and the 35A fuse blew as soon as I switched the ignition on. Not convinced myself that I've missed something here (the garage is getting cold in the evenings). So, I've reverted back to Pos Gnd for the time being until I can fathom out what's going on. Any ideas?? It's a MKII 850 with Boyer but electrically standard apart from that.......I need to take the load off the Prince of Darkness charging system as our Southern Hemisphere winter commutes are well underway, so LED bulbs are the first and cheapest step. I'm already running a nice fat gel battery. Cheers - Nick
I had done the conversion and had no issues. However I did go thru the whole bike removing unneeded wires and making sure the nothing was grounded after the conversion that shouldn't be. Are you running standard zeners and rectifier?

Here is a list of things to check.

1. Standard zeners will need to be replaced as they are pos gnd and create a short if the battery is reversed.
2. The standard rectifier will need to be rewired. Installing a reg/ rec unit will solve both zener and rectifier problem.

3. Check and follow all wires coming into and out of the ignition switch.
4. I had removed the blue can completely.
5. Check and follow all wires connected to the battery.
I have converted my MK11A to negative ground but fitted a Boyer powerbox to do away with the zenor etc.
Can you just change the ignition to negative ground?, would you not need to change all the other electrical components as well,e.g. the ground wires from lights, switches and other parts so they were all positive fed and negative ground.

You would need to change anything that requires the current to flow in a certain direction. Any device, such as the boyer box, LED's, diodes, electrolytic capacitor, etc.

The lights are incandesant and will function whether it is neg or pos ground without modifying the wires. The main change I did to the light wiring was to replace most of the red gnd wire with a black ones.

The coils as well will need to be rewired as they do have a neg and pos terminals and will need to be wired to reflect the change.
Many thanks for all the posts - I'm running pos gnd again for the time being. The 32 year old wiring loom is starting to give me issues that require constant investigation. So, I think a rewire and Boyer powerbox is on the Christmas list. Cheers - Nick
Well, a non-functioning front brake switch meant I was under the tank again at the weekend hunting the broken wire/connector that proved to be the culprit. Whilst I was there, I removed all redundant connections and had another go at Neg Gnd. I rewired the Boyer/coils as per the BritCycle diagrams, put in a neg gnd Zener, rewired the modern bridge rectifier (by switching the two non-alternator connectors) , removed the 2MC cap and jumpered the wires (but left the red "earth" connector hanging). I checked the wiring from the ign switch and battery & then switched the battery connections. Unfortunately the ign light glowed for a couple of secs before the 35A blew again........other than putting a second more detailed search into the wiring loom, have I missed anything?? Reverting back to Pos Gnd has everything working beautifully!
Do I need to rewire the WL assim? What's the small black box with two connectors sitting behind the unused ballast resistor?
Any suggestions welcome! Cheers - Nick
hal20308 said:
What's the small black box with two connectors sitting behind the unused ballast resistor?

Probably the ignition condensors for the original points setup.
If memory serves me rigth I did rewire the WL Assim. By jumping the wires on the 2MC cap, do you mean you connected the 2 connecting wires together? If so that may be an issue, I removed mine completely, they should not form a closed circuit.
The warning light assimilator operates on AC current (non-rectified), so it should not need wiring alteration. All it does is take current directly from the alternator output before the rectifier
Thanks for all the suggestions folks.
Regarding the 2MC cap - it has two brown wires on a common lug which is what I jumpered together. The red "earth" wire I just tied off so it didn't short on anything. I think I've seen earlier posts which suggest you get no juice to the ignition unless the two common wires connected to the 2MC are joined? Cheers - Nick
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