Negative ground digital speedo on Positive ground loom

[Easy-X]

It's Friday. Brain has given up. Insufficient beer supplied

Working on an early '70s Triumph with a positive ground loom and attempting to add a Koso digital speedo (custom wheel hubs, no mechanical speedo drives present.)

The instructions call for permanent +12V, switched +12V and ground i.e. very conventional. With this Triumph the frame is +12V from the battery with permanent power (via the loom) going to the 0V of the battery and so switched power is also 0V.

So either some sort of circuit rearrangement required or - the extreme option - changing to a negative ground loom. Note the Koso speedo is in an isolated case so "metal touching metal" not an issue and the Boyer Bransden ignition is happy with either negative or positive ground systems.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

So permanant +12v to the frame. A SPNO relay controlling the switched +12v, earth wired to a permanant "live" wire on the bike.

Relay is just a switch, it'll switch anything. I have relay controlled AC lighting on my trials bike (DC from the switch to trigger the relay).

EDIT: Re-upped diagram due to brain fart.
https://www.bikechatforums.com/download.php?id=106645
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[WD Forte]

I'd convert it to neg ground
It's pretty straightforward with less chance of confusion.
Having a conventional system would also give you the
ability to easily add or modify gadgets and stuff later if wanted/needed.

fuck the 'classic innit mate' shite, i wouldn't cling to pos ground
any more then I'd stick with points ignition, AC and incandescent blubs
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bikers smell of wee

[stinkwheel]

He could run gadgets using his switched +ve relay above.

Good quality LED bulbs aren't polarity sensitive any more.

There may be reasons for using AC lighting. In my case 1) It works really well and 2) The DC only runs the ignition (and a relay) on that particular bike meaning I get away with an outrageously tiny battery
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

Thinking on it I was going for a semi-concealed, minimalist LED tail light. As it's two-stage I'd face a similar problem so that's 2 relays now

If I go with negative ground I could either swap the red & brown over, maybe add a bit of black heatshrink the "new" ground, or burn money getting a later model loom.

I'll give the bike a long hard stare tomorrow.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

[WD Forte]

I converted the moby from AC shite lights and points ignition
to run with no battery and leds that actually gave out light nae bother
I assume we're talking '71 T120 or similar?
well I just browsed a couple of contemporay diagrams and
it's not much more complicated and in some ways even easier

Yes there are work arounds/get you home methods
but they're short term IMO
I reckon having a mixture of grounds is a bad practise when you can have a regular conformal system ready to use easily available,
off the shelf stuff that can easily be swapped out, modded and upgraded
It also sticks to the K.I.S.S. rule.

I rode these old bikes when they were commonplace, they had crap electrics even then so I'd have no hesitation in upgrading them
if I was forced to own one.
but it's your shitty old bike, do what you want
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bikers smell of wee

[Easy-X]

[Easy-X]

For now I'm just swapping the battery terminals over on the loom. Red = 0V, Blue/Brown = +12V, White = +12V switched (using a Lucas loom.)

I disconnected everything and wired up just the brake light and that worked out fine. Now I'm working through the wiring diagram and thinking through the implications. Mainly just redoing the ignition system.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Nobby the Bastard]

What sort of charging system does it have? It would be positive ground and so some sort of swapping of wires may need to be done there too.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Easy-X]

[Easy-X]

Back end re-done as negative ground, just need some cable ties:

https://i.imgur.com/EAS0LaP.jpeg

Kicked it over and getting spark.

Following the minimalist aesthetic, stripped the front loom to the essentials:

https://i.imgur.com/bS5BZFB.jpeg

To do: wire up a hi/lo beam switch, horn button, speedo and ignition.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter