Wiring, 12v, positive earth butchery.

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
Mick D
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Location: Aberdeenshire

Re: Wiring, 12v, positive earth butchery.

Post by Mick D »

Hi

Before you go too far down the negative earth route you need to work out how you are going to reverse the connections on the points capacitor. The one fitted by design is an electrolytic and hence polarity sensitive - easy enough to wire in a replacement but retaining the original would be challenging due to it's construction.

Why the desire to go negative earth?

Regards Mick
Callyloz_LAPSED
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Location: Portsmouth, England

Re: Wiring, 12v, positive earth butchery.

Post by Callyloz_LAPSED »

Hi Mick,

To be honest, i saw nothing about the points in the write up when swapping from pos to neg earth. Saw the coil, ammeter horn, which all seemed easy enough to sort. So made sense to go neg earth due to potential for LED's etc, but if it requires changing any other parts, i'm not really that fussed.

So yeah, happy enough to maintain the current positive earth if that is the case.
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clanger9
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Re: Wiring, 12v, positive earth butchery.

Post by clanger9 »

You don't need that big electrolytic capacitor if you've got a battery fitted. That capacitor is for battery-less running...
1989 Moto Morini Dart 350
1993 Ducati 750SS
Callyloz_LAPSED
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Location: Portsmouth, England

Re: Wiring, 12v, positive earth butchery.

Post by Callyloz_LAPSED »

I assumed by points capacitor, he is reference to the condenser? It didn't make sense to me, only from my Morris Minor daya od converting to negative earth, where you didn't have to do anything with the points syatem.

That blue capacitor is absolutely going to be disconnected, so no fear about that.
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clanger9
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Re: Wiring, 12v, positive earth butchery.

Post by clanger9 »

Ah, no worries then!

The points condenser isn't bothered about polarity (it's not electrolytic), so no difference whether positive or negative earth. Just need to check the coil polarity.
It'll still work with the coil polarity incorrect, but the right polarity ensures the best spark...
1989 Moto Morini Dart 350
1993 Ducati 750SS
Mick D
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Re: Wiring, 12v, positive earth butchery.

Post by Mick D »

clanger9 wrote:The points condenser isn't bothered about polarity (it's not electrolytic)
Every day's a school day :)

I assumed from it's looks that it was an aluminium foil electrolytic :oops:

Regards Mick
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clanger9
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Re: Wiring, 12v, positive earth butchery.

Post by clanger9 »

No shame needed Mick!

They do look like an electrolytic, but it's just a a paper-wound 0.2uF high-voltage capacitor.
So, one less thing to worry about when swapping the polarity... :beer:
1989 Moto Morini Dart 350
1993 Ducati 750SS
Callyloz_LAPSED
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Joined: Sat Feb 13, 2021 7:00 pm
Location: Portsmouth, England

Re: Wiring, 12v, positive earth butchery.

Post by Callyloz_LAPSED »

Hi Folks,

A wee update on this.
I got it all connected over the last few nights, then today has a chance to get the bike back together and try and fire it up.
It wasn't very happy to start with, which left me scratching my head as the chap who i bought it from rode it to my house, so assumed the worst with the install (installer error).
Having had a look through the bike a bit more, i found a quite funny issue...the carb choke slide had been installed upside down. So when fully up, it was still half closed. Explains why the choke cable was really slack when closing the choke off. No idea how long it has been like that for, but can't have been running all that well. I will need to look at the carb adjustment settings now as i am sure they will have been altered to get it to run.

Anyway, i believe the issue i had was that the frame was not being earthed well with the rectifier and battery🤦🏻‍♂️. I had the wires connected up, but the seat wasn't on and the rear frame was "loose" from removing it. I only really realised as the tail light wasn't earthing out/working. Anyway, the rectifier is attached to the battery mount, which is attached to the rear frame, so yeah, additional wire, fired straight up 😂
So it is now negative earth, ammeter appears to be doing what it is supposed to and the bike fired up nicely and ran alright (but will probably need a wee carb tune).

Thanks very much for the info thus far, i am sure i'll have lots of questions soon, perhaps look at electronic ignition next 👀
WiltshireMike
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Location: Wiltshire UK

Re: Wiring, 12v, positive earth butchery.

Post by WiltshireMike »

I've just done a 12v & electronic ignition (Boyer) conversion, helpfully assisted by this thread:
https://www.ifixit.com/Guide/AJS-Matchl ... ion/117791

The wiring is now much simpler, with a much reduced risk of overcharging, plus it now works a full 50W headlamp.

I used the following bits:
Regulator - eBay 313328016585
Coil - eBay 222966643156
Battery - https://www.thebatteryshop.co.uk/index. ... roductid=0
Ignition - Call Boyer on 01622 730939 or info@boyerbransden.com and order Kit00045
Horn - eBay 402507884986
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clanger9
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Re: Wiring, 12v, positive earth butchery.

Post by clanger9 »

Brilliant, glad the guide was helpful! :D
Please feel free to make edits/suggestions if anything was unclear :beer:
1989 Moto Morini Dart 350
1993 Ducati 750SS
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