Negative earth rewire

I’m musing shall I go negative earth wiring when I eventually get around to doing a rebuild. I know I could just as simply go back to the then norm of positive earth, but I am starting from scratch with my own simplified harness - and also the LED bulbs I already have are -ve earth only.

However, a couple of quick questions bearing in mind this will be a very minimal system. Magneto ignition and 2 wire Lucas alternator.

My intentions are to use an ammeter in the system as it looks correct for the period.

I want to leave the stop light and the horn live - shall I fuse each separately, or one fuse covering both circuits?

Shall I fit a fuse between ammeter and battery, or ammeter to light switch? Or both?

From the 3 way light switch I already have, off, pilot, pilot and headlights, I will fuse the circuit for the pilot, tail and clocks

Then a fuse between the switch and the dipswitch

I am using a Podtronics unit I already have and thus doing away with a zener diode. Anything I’ve forgotten?

Put a 20 A fuse in a sole return wire, near to the battery earth terminal.

Please yourself about other fuses.

If putting multiple fuses in then an Eastern Beaver PC8 fuse panel or similar is worth a look, gets all the fuses in one location. They now have the PC8R which has some circuits relay activated. Have rewired my ES2 with the non relay one and is a tidy unit.
The Horn has huge current draw compared to anything else, it is normally wired in before the ammeter with all other load through the ammeter. If putting multiple fuses I would fuse the horn separately.

Keep it simple, with a magneto the wiring can be kept to a minimum, I just run one fuse on my whole system but I have kept with + earth, I also keep my earth wire outside of the main wiring harness, most of my electrics are under the seat in the tool tray of my Featherbed and only 4 main wires running up to the front of the bike and 1 earth wire, in 45 years of running this set up have had no problems, I run a small dirt bike battery also under the seat which I share with my Honda dirt bike, but I don't run day light lights so really only a very bright brake light during the day time, any bikes made before 79 no need for day lights running in my state, but good to have working light if caught out late.
As I say keep things simple and have less problems down the road.

Ashley

Flatspot said:

I’m musing shall I go negative earth wiring when I eventually get around to doing a rebuild. I know I could just as simply go back to the then norm of positive earth, but I am starting from scratch with my own simplified harness - and also the LED bulbs I already have are -ve earth only.

However, a couple of quick questions bearing in mind this will be a very minimal system. Magneto ignition and 2 wire Lucas alternator.

My intentions are to use an ammeter in the system as it looks correct for the period.

I want to leave the stop light and the horn live - shall I fuse each separately, or one fuse covering both circuits?

Shall I fit a fuse between ammeter and battery, or ammeter to light switch? Or both?

From the 3 way light switch I already have, off, pilot, pilot and headlights, I will fuse the circuit for the pilot, tail and clocks

Then a fuse between the switch and the dipswitch

I am using a Podtronics unit I already have and thus doing away with a zener diode. Anything I’ve forgotten?

Click to expand...

IMHO, multiple fuses confuse troubleshooting and add nothing. You should have one fuse in the line from the battery that is not ground. That fuse could be an AGC 10 or an SFE 20. There is no need for a British Spec 35 amp fuse as you are using a magneto and LEDs. If using the standard inline fuse holder, then any of the AGC fuses will fit but only SFE 20 is the right length. If using the standard horn, then AGC 10 is good. If using a modern horn and all LEDs, AGC 10 is overkill.

When I wire bikes, I use a AGC 5 during wiring testing in case I make a mistake - it will prevent wire damage. Then on initial run testing I use an AGC 10. Once everything is tested and the bike is roadworthy, I switch to an SFE 20 - and that's all with standard components.

I use 28-strand wire for the Brown/Blue, Brown/White, and Ground. 14-strand is fine for the rest (original harnesses only use 14-strand).

If using standard colors, Brown/Blue from battery to fuse. Brown/Blue from fuse to Ammeter. Brown/White from Ammeter to master switch.

This may be of some help to you: https://gregmarsh.com/MC/Wiring.aspx

This too: https://granttiller.com/richard-foster


If using negative ground, black wire for ground, if using positive ground then red wires.

Personally (being a Luddite) I’d keep it as simple as possible.

I believe Grant Tiller has some suitable example schematics on his web site?

The best thing you can do is keep the mag, then you have super reliable sparks that are totally independent of the rest of the electrical system.

With a minimalist harness, only doing charging and lights, I’d personally see one fuse as perfectly adequate.

If you skip the ammeter, you get a much simpler circuit. I like the battery status monitors that Aoservices and Paul Goff sells as they are much more useful.
I usually fits only one fuse between battery and earth. Big enough to handle the horn.
What many miss is reliable earth connections. Worth thinking of how current goes.
As you have magneto and LEDs, the regulator/rectifier will burn a lot of power so it has to have a large heat sink and cool air.

Mike40M said:

If you skip the ammeter, you get a much simpler circuit. I like the battery status monitors that Aoservices and Paul Goff sells as they are much more useful.
I usually fits only one fuse between battery and earth. Big enough to handle the horn.
What many miss is reliable earth connections. Worth thinking of how current goes.
As you have magneto and LEDs, the regulator/rectifier will burn a lot of power so it has to have a large heat sink and cool air.

Click to expand...

Or, if all LEDs and low current horn(s), consider no alternator/charging circuits at all, an AGM battery, and a trickle charger between rides. An 9ah AGM will run LEDs much longer than it sounds like you will be riding the bike. If you really want the charging circuits, use a standard 10 amp, single-phase stator (2-wire) - that is already too much "power" for what you want to do!

You can always put in an ammeter connected to nothing for looks - if you wire normally and the system is fully charged and working normally, the ammeter will remain in the middle almost all the time, just like if it is not connected.

I have an ammeter type headlamp unit which I will be using, along with an ammeter, so not bothering to wire it into the circuit does seem a reasonable idea. I have a Podtronics regulator to use, the same as on my T160 and Commando. I also have a small Yuasa 12v 2.4ah AGM battery to hide away under the hump.