Ignition Switch Wiring ?

[Adrian S]

Due to a fight for position between my dash and my ignition barrel I’ve instead opted for a dash mounted ignition switch. Easy job I thought ! That was until I lopped off the old wires and found I had one spare wire which I have no idea what it’s needed for. The old ignition switch has 5 wires and as far as I can tell they are:-
+12V
Accessories
Ignition
Start
Earth (or at least this is what my multimeter is telling me)

My new ignition switch has the following:-
2 Pins for +12
Accessories
Ignition
Start

I tried just connecting up +12, Ignition, Accessories, and Start. When I go to start I can hear the relay click but no cranking.
I thought I’d try the old switch again and just not connect the Earth wire – same thing…the relay clicks but no crank. When I connect up the earth wire, she fires into life.
So my first question is what is the earth wire for and where should I connect it (no smart-ar$e answers please).

My second question is that I wanted to hook up a red starter button. Would I need to run this off the Ignition pin from the switch? I assume the current through this will be OK for starting ? If I connect it to +12V then it would try crank even when the car is off if the button is pushed. Anyone done this already ?

Thanks,
Adrian.