"Inverting a switch"
The thing that i need to make this work is that the ignition lock needs to be open (let eletricity pass trough) when the key is turned.


First some terminology:


When you close a switch electrical current can flow.
When you open a switch the load is switched off.


You must have measured the switch incorrectly. All ignition switches will isolate and turn off the ignition system when in the off position.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Switch logic.







simulate this circuit

Figure 2. The ignition switch will have two "normally-open" (in the off position) contacts. The ignition contact will close when the switch is turned clockwise to the mid-position and the sprung starter contact will close when fully clockwise.



What you need

It seems as if you have bought the wrong switch. If you want to switch off a magneto then you need to short-circuit the points (spark switch) so that it is always connected to ground.



Figure 3. Lawnmower ignition circuit with kill switch. Source: DenGarden.com.

You want a switch that will be closed when the ignition is removed. I'm sorry, but you have bought the wrong switch. The price on the eBay link was US$2.60 so I don't think the error will cost you too much - probably more for postage.



Another possibility



Figure 3. Using a normally open (NO) switch to kill the engine.

If you are able to add the switch you bought at position 1 or 2 it should do what you want.