Red warning light stays on while riding — 1969 Commando Fastback 750

[Lorenzo]

Hi everyone,
I have a 1969 Norton Commando Fastback 750 and I've noticed that the red warning light on the headlight stays on both when the bike is stationary and while riding. The bike has been fitted with a Boyer Bransden electronic ignition replacing the original points, but the rest of the electrical system is original — no Boyer Power Box has been fitted.

I have always understood that on this specific year the red light is simply an ignition warning light and is not connected to any charging indicator function — so it staying on may be normal for this model.
Can anyone confirm what the red light on a 1969 Fastback is actually wired to? Is it purely an ignition light, a charge warning, or something else? And should it go out once the engine is running?

Any advice from those with experience of early Commandos would be very much appreciated.
Many thanks

 

[concours]

Edit: I default to Les's correction.


That light is controlled by the assimilator, which monitors AC voltage from the stator.

You could have:
1) a faulty assimilator
2) broken wires from the stator
3) faulty stator
4) faulty rotor.

TEST, don't guess.

Do you have a voltage meter to test the AC voltage?
Are you familiar how to use it?

 

[Lorenzo]

That light is controlled by the assimilator, which monitors AC voltage from the stator.

you mean that it should be off when riding?

 

[concours]

you mean that it should be off when riding?

Correct. Normally, it goes out as soon as the engine starts.

 

[L.A.B.]

That light is controlled by the assimilator, which monitors AC voltage from the stator.

A 1969 model doesn't have the assimilator, the red warning light pre-1971 is for main/Hi beam. It should be connected to blue/white and red.

Andover Norton - WARNING LIGHT, RED, HEXAGON LENS (38189) - 99.0568

WARNING LIGHT, RED, HEXAGON LENS (38189)

andover-norton.co.uk

 

[APRRSV]

A 1969 model doesn't have the assimilator, the red warning light pre-1971 is for main/Hi beam. It should be connected to blue/white and red.

Andover Norton - WARNING LIGHT, RED, HEXAGON LENS (38189) - 99.0568

WARNING LIGHT, RED, HEXAGON LENS (38189)

andover-norton.co.uk

I thought the Hi beam warning light was green. Maybe wrong. I was a long time ago.

Ed

 

[L.A.B.]

I thought the Hi beam warning light was green.

No, not pre-71, 38189 (99-0568) is red.

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

Haven't we done this one before.

A

Post in thread 'I'm a newbie wishing to know what I have. (2013)'

Aug 27, 2016

Wasn't the pre-71 Commando warning light green. It was a high beam indicator as I remember.

Ed

• APRRSV

 

[Lorenzo]

A 1969 model doesn't have the assimilator, the red warning light pre-1971 is for main/Hi beam. It should be connected to blue/white and red.

Andover Norton - WARNING LIGHT, RED, HEXAGON LENS (38189) - 99.0568

WARNING LIGHT, RED, HEXAGON LENS (38189)

andover-norton.co.uk

it seems the red light is always on, no matter if the lights are on, main or high beam or off at all.. BTW I noticed that the speedo bulb is blown, but not sure if this is the reason of wrong functioning..

 

[L.A.B.]

BTW I noticed that the speedo bulb is blown, but not sure if this is the reason of wrong functioning.

Probably not as that's a different circuit.

 

[L.A.B.]

Are you using an LED headlamp bulb as apparently that can cause the warning lamp to malfunction?

 

[Lorenzo]

Are you using an LED headlamp bulb as apparently that can cause the warning lamp to malfunction?

thanks: I am not using a LED headlamp..

 

[L.A.B.]

I'd check the wiring to the warning bulb then.

 

[Lorenzo]

I'd check the wiring to the warning bulb then.

you mean that if the red light is always on there's a malfunctioning?

 

[L.A.B.]

Yes one side of the light should be connected to the headlamp high beam wire (blue/white) and the other side to earth/ground (red) so it should only be on when the high beam is on.

 

[L.A.B.]

if the lights are on, main or high beam

Note that main is high beam, the other is low or dip beam.