1954 BSA B31 Plunger wiring loom

[briancairns]

Hi,
I put a wiring loom on bike ( see attached) . The bike had no electrics whatsoever when I got it.
I converted to 12v, bulbs, rectifier, mag, bulbs etc. with negative earth and negative earth rectifier.
Everything is working: Main beam, high beam, light switches, pilot light, rear light, break light and light for speedo.
However can't get the horn to work ( 12v) nor the ammeter.
If i put a battery straight across the ammeter it works.

I have a couple of questions;
Is the wiring loom pictured for negative earth ? or does it mater?
Also do i still have to earth the main beam light fitting and pilot light with the head lamp casing?

[idie]

I am surprised that you didn't,t fry the ammeter putting it across the battery. The headlamp reflector needs a earth return back to the shell . Normally there is two wires for the horn from the loom , one live and one back to the horn push. The feed for the lights has to come off the ammeter the opposite side to the feed from the battery. If not although the light will work the ammeter will show nothing. I take it the you are referring to a voltage regulator and not a rectifier which were not fitted on a B31 until 1959.











,

[briancairns]

Hi Idie,

Thanks for advice, luckily  did not fry ammeter!!
Sorry , I was referring to the voltage regulator .
I will try your advice tonight and let you know how it goes.
As you can see from the photos, there are 3 wires connected to the horn spades ( came this way when I bought the loom) and then another separate black wire coming from the same area ( see wiring diagram) which is assume is the horn push. The horn push wire is black ( but yellow and red on diagram) as stated and is long enough to connect to to all one light /dipswitch/ horn push on handle bar.  I assume the second photo is the horn push (black button)

[Spaceman]

I believe for a 1954 B31, the wiring should be +ve earth but changing to -ve earth isn't a big issue. The ammeter should be connected between the output from the regulator output (A terminal) and the battery +ve terminal - in the Lucas wiring diagram, it is the black/white from terminal A to the lighting switch T3 and from there on to the ammeter, and the yellow/black wire from the ammeter to the battery +ve terminal. The ammeter will then display the current from regulator to the battery.

The horn should be connected to the battery +ve terminal and then to the horn push and then to ground. The other yellow/black wire from the battery should go to the horn (feed) and then via the yellow/red wire from the horn to the horn press (button) with another wire from the press to ground.

As in most BSA wiring systems, the return from all the lights is through the tinware and frame. However, I always use a separate earth return wire back to the battery earth and never use the tinware or frame as you can never be sure there aren't any voltage drops due corroded connections of one sort or another.

[Derek996]

Up to 1952 they were -ve earth but from 1953 were +ve earth. The original voltage control unit would work with either but a modern electronic regulator is made for either -ve OR +ve earth, so the bike will have to be wired to suit.
Attached are both the +ve and -ve earth circuit diagrams of it helps.

[briancairns]

Thanks Dereck,
I have a negative earth electronic regulator.

I think your negative earth diagram follows the wiring loom diagram that i posted?


Cheers

Brian

[briancairns]

Hi all,

I have squiggled on the wiring diagram which i have attached
The horn press wire  yellow/red is actually black  ( black squiggle) on the loom and is in the same place. There is no other horn press wire.
There are 2 yellow/red wires attached to the horn switch spade and I received the loom with the spades connected. I have marked this with a blue squiggle.

Please excuse my ignorance , as I am new to this .

Getting a little confused.
I followed the diagram exactly .

Many thanks to all

Brian

[Derek996]

The horn feed (yellow/brown) should be live from the battery (or the battery side of the ammeter) and should be connected to one of the horn terminals. The yellow/red wire should go to the other horn terminal and the other end of it should go to the horn switch, although apparently it is black at that end in your loom. If the horn is connected and the battery fitted dabbing the back wire to earth should sound the horn. If so connect it to the horn switch and it should work.

[Spaceman]

Normally, the horn press will earth against the handlebars and so a separate wire is not normally needed. However, you would need to test that this happens when you press the button.

There should be 2 x yellow/red wires emerging from the loop which are two ends of the same wire. The yellow/black wire for the horn feed comes from the battery +ve terminal. One yellow/black wire goes to the horn and the other goes to the horn press button. As  said, pressing the horn button should earth its yellow/black wire to ground causing the horn to sound.

[briancairns]

Thanks all

Fantastic wealth of information!

Once again Thanks

Brian

[rhyatt]

Does this dynamo need converting from pos earth to neg earth at all?
Might need flashing to convert

[briancairns]

Thanks, I've already flashed the mag

Brian

[briancairns]

Hi All,

Just to let you know I got everything working fine.

Thanks so much to you all for the wonderful advice .

Brian

[Rog1]

Brian

In case you haven't noticed, in your first photo it looks like the insulation on the yellow/red wire is broken, just by your fingers; I can see the copper.

Roger

[briancairns]

Hi Roger
Thanks I spotted that and sorted it .
Cheers Brian