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Posted: Sun Dec 01, 2019 11:42 am
by Stephen Smethurst
Done everything to this bike including engine rebuild and straightening the frame in my jig. Replaced several electrical components with standard like for like. Recon dyno as well. Made a new wiring harness. Maybe I'm wrong but I thought an ignition switch would stop current going to the distributor and coil. Turned off it continues to run and my assumption is current from the dyno is not isolated. Switch turned off and turning the light switch to the right does stop it running. Cleaned the contacts of the Lucas regulator which makes no difference. Maybe thats how it works...any advice much appreciated.

After tea and biscuits I thought I should high light the fact that the light switch 31315 shown on Draganfly website was fitted in lieu of the
the broken seven pole switch. This switch has six poles however, the wiring diagram shows seven poles one of which is not used.
All circuits have continuity and receive acceptable voltage.

Thought I'd get this one off my chest as well. There are three wiring diagrams for this model. One major difference relates to the positive earth.
The last diagram indicates shows earth wire from battery to regulator with one earth connection followed by a second earth.
The other two diagrams show a wire from battery to earth and a wire from regulator to the same earth point. Which is best ?


Posted: Sun Dec 01, 2019 12:38 pm
by JohnnyBeckett
it can be the switch in side that is still make contact wen you turn it off or the wiring is wrong somewhere i would check the switch first


Posted: Sun Dec 01, 2019 6:39 pm
by alan.moore
I agree that, if the wiring is connected as per the diagram, it is likely to be the headlamp switch still giving a feed from the dynamo to the coil as you say. Having looked at the wiring diagram this is my take on how it SHOULD work

The wiring diagram with the 7 pole switch shows the switched power feed is from Terminal 3, via the ignition switch, to the coil terminal SW.

It shows a second wire from The SW side of the coil to terminal 7 and from there to one side of the Red Spot lamp in the ammeter. There is also a wire from the the D terminal wire of Dynamo (power feed from dynamo) to terminal 6 and from there to the other side of the Red Spot lamp.

It is my understanding that this circuit causes the Red Spot lamp to illuminate when the ignition is turned on i.e. power feed from battery via ignition switch travels via coil SW to terminal 7, through Red Spot lamp and then via Terminal 6 to Dynamo D wire which, as the Dynamo is producing no charge, is earthed via the charging circuit.
When Engine starts and Dynamo is charging the Red Spot now has a power feed from Dynamo D wire via Terminal 6 AND battery power via Terminal 7 and as there is now no potential difference across the bulb (so no current flow) the bulb goes out.

Now for the bit I am not quite sure about but it makes sense to me....When you switch the ignition off that cuts the power (current) from the battery to the SW side of the coil. Whilst the second wire to the coil SW, which is now being fed Dynamo power via the Red Spot bulb circuit described above, the Red Spot bulb (according to an article on the Vincent owners clud site) is only rated at 0.6 watts so it only draws 0.1amps which is not enough current to operate the ignition coil and therefore the engine stops.

So...first thing would be to disconnect the wire that goes from Coil SW to Terminal 7 and isolate / insulate the disconnected end. (It's only part of the Red Spot lamp circuit so should not effect anything else). If what I have said above is correct the ignition switch should work normally.

I think the most likely cause of the problem is that the light switch is providing battery power to terminal 7 or 6 when it is in the off position, you could check this using a volt meter.

As for the earth wiring I would wire the battery terminal to the earth point on the frame and use a separate wire from the regulator.

I would also suggest adding some fuses in the battery and charging circuit from the Regulator. Have a look at Simon's website here for some pointers ... iring.html



Posted: Mon Dec 02, 2019 6:44 pm
by JohnnyBeckett
HI Stephen the first thing i would do is to fit fuses if you do not have them it will stop you frying the wiring loom


Posted: Tue Dec 03, 2019 7:16 pm
by Stephen Smethurst
Thank you for all responses and Mr Moore in particular. His description of how circuits work and inter connect is accurate and easy to understand
provided one understands potential difference, voltage drop and so on . DC generators play no part in the ignition system other than acting as a temporary earth for the red light. It charges the battery from which the ignition system draws current. Fuses are circuit breakers and do not run hot. Hot fuses and warm wires are indicative of resistance of the current flow. Switches turn off current supply. All sounds obvious but my oh my, finding the problem can be vexing.
After morning coffee I concluded the problem must be the replacement headlamp switch. Mr Moores description confirmed it. Found the old
switch and several from various BSA's. After tea and biscuits the renovated old switch worked well. The problem has gone away.

From my website you will note that I renovate castings using mass vibration. This skill brings in other work. Restoration of the
Square 4 and the Vincent before it are examples however, they really test me. It really does. This Square 4 had hydraulic lock..could not kick it over. The Vincent had "The Korean war spindle" Despite having an engineering background the lack of product knowledge is a serious hand brake.
There isn't anybody local to ask either.

Thanks again.