Lucas A10 wiring loom

[Catz]

I've bought a brand new Lucas wiring loom for my 1960 A10 but i'm confused by the diagram that came with it.
It says for A10 1954 - 1962 swinging arm frame but the diagram shows negative (-ve) Earth. Isn't the 1960 A10 +ve Earth? What should i do, just wire the black -ve wire to the +ve terminal of the battery and the red +ve wire to the frame? Anyone else bought one of these looms and if so what's what with it?
WP_20221104_17_42_33_Pro by XJR1200 TIGER, on Flickr

[Spaceman]

Just reading the Haynes manual, it says the polarity was reversed in 1951 so the earlier ones had +ve earth and the later ones had -ve earth - or was it the other way around?

[Catz]

Oh yes, the good old Haynes book of Lies.
You are correct that the polarity was reversed in 1951, as it states in the book of Lies and Trickery, but at the start of the Electrical equipment chapter in said book it states Polarity of system 1947 - 50 negative earth and 1951 0nwards positive earth.

[DAVE BRADY]

Hi,

Even late 12v A65s are still +ve earth.

Dave.

[EDDIE SIMPSON]

red is normally earth so the wiring harness looks correct and is positive earth.

[Catz]

red is normally earth so the wiring harness looks correct and is positive earth.

But on the picture it says "Earth" with a negative with a black wire.

[JulianS]

If you are unhappy withn the harness I suggest send it back to the supplier, or at least ask them about it.

The swinging arm models were certainly positive earth.

Below wiring diagram from the 1960-62 owners manual.

[Catz]

Thanks for the diagram.
You're right, i'll take the loom back on Monday.

[EDDIE SIMPSON]

its hard to read the diagram but that earth is a misprint. i can see the black[ live ] wire goes to the ammeter, horn, regulator and rear brake switch which is correct. i cant read the headlamp switch wires but one should be live from the ammeter either black or brown.
the other red wire goes to the frame post by the battery usually.

[Spaceman]

It's not a very complicated wiring harness and, assuming the +ve and -ve battery connections on the Lucas wiring diagram are simply labelled the wrong way around, all you need to do is to check the harness wires and connections against the wiring diagram from the Owners Manual, and check all the harness connections fit to where the components are on the bike.

Apart from possibly the colours of some of the wires, I'm not sure there is much of a difference between the -ve and +ve earth versions of the wiring harness.

[Catz]

Thanks for the encouragement lads, much appreciated. Here's a better picture of the Lucas diagram. Hope it makes a bit more sense visually.
WP_20221105_08_33_31_Pro by XJR1200 TIGER, on Flickr

[Spaceman]

As far as I can see, the colours in the diagram are not completely consistent with the original wiring harnesses for either the positive or negative earth systems. For example, neither had a red/black wire to T2 as far as I can see.

Unless you are after 100% authenticity with the original wiring harness, the actual colours used don't really matter as long as you can work out which wire and connector is which. As far as I can see, the wires in the Lucas diagram appear to correspond to those shown in the wiring diagram from the owners manual and, as long as the wiring harness fits your A10 with the right connectors in the right place, it should do its job properly.

[Servodyne]

I've used one of these looms and the only fault was the battery terminals + & - had been labelled the wrong way round. I think the confusion started with the Owners manual diagram as posted by Julian. It shows the black wire going to the positive terminal on the battery and going to earth, then a brown wire going to the neg battery terminal.
Perhaps Wassell thought BSA had screwed up with their diagram.

[Catz]

As far as I can see, the colours in the diagram are not completely consistent with the original wiring harnesses for either the positive or negative earth systems. For example, neither had a red/black wire to T2 as far as I can see.

Unless you are after 100% authenticity with the original wiring harness, the actual colours used don't really matter as long as you can work out which wire and connector is which. As far as I can see, the wires in the Lucas diagram appear to correspond to those shown in the wiring diagram from the owners manual and, as long as the wiring harness fits your A10 with the right connectors in the right place, it should do its job properly.

Thanks for the info, and no i'm not going for 100% authenticity.

I've used one of these looms and the only fault was the battery terminals + & - had been labelled the wrong way round. I think the confusion started with the Owners manual diagram as posted by Julian. It shows the black wire going to the positive terminal on the battery and going to earth, then a brown wire going to the neg battery terminal.
Perhaps Wassell thought BSA had screwed up with their diagram.

Thank you too. All good to hear.

[EDDIE SIMPSON]

now i can see the diagram better i can see some problems with this loom.
its showing the regulator earth to a black wire and the horn earth to a black wire with a brown live. it is all wrong in my opinion.
you can easily modify it for black live and red earth by belling out the live and earth circuits and modifying the loom. however as already suggested take it back and get your money back