Fitting a kill switch to a 1954 Norton Dominator 88 De Luxe.

I assume you have the Lucas k2f magneto points end cap #458619 ? 

It has a brush that grounds the points screw when you wire it to a horn/kill switch button.

I think taking the end cap off might be the best place to start.  As Mikael says, it needs the brush that grounds the points, but maybe the carbon brush is missing or worn out?

.. just connecting a bit of wire to the terminal on the mag cap and seeing if earthing that to the engine stops it. If so, it's your handlebar switch or wiring. If not, the brush in the mag end cap isn't making proper contact.

hello now on my Norton dominator model 88 of 1954 vintage I  have fitted my kill switch in the tool try next to the left hand side just under the seat with the switch togel sticking out ext to the seat bottom edge  and works well forwards for on and back for off and my Norton Manxman 650 fitted up the same way but has a handlebar kill switch as well next to the throttle kill switch wire colour is white but i fitted the wire for the handle bars with a white with red tracer wire so I then know witch is witch wire and to where,  now magnetos have two earthing bushies  one on the end cap cover and one fat brush at the other end of the magneto  in a screw cap do check both of them  as they do ware out,  yours  anna j  

On a '54 Dominator the kill switch, or stop button, was fitted, as Anna has placed her's, on the left side of the tool tray. Originally, it would have been just a horn push.  I like the idea of a button on the handlebars,  in an emergency you don't really want to take your hands off the bars !

I prefer a switch over a button. When the throttle slide hangs at 1/3 open on the Manx, it makes it easier to raise my right hand notifying fellow racers that I'm going to stop. Left hand needed for disengaging the clutch.

is operating the switch?

Left thumb toggles switch before pulling clutch.