Gentlemen; while I never actually worked on a Spit (just too young) I was nevertheless an RAF Air Radar Tech for six years, followed by another ten as a UK-licensed Aircraft Radio Engineer and worked for three airlines during that latter period, and I will guarantee that - in the UK, at least, during that time period - a contactor was a heavy-duty relay, such as would be employed on the provision of 12 volt power to an old tube-type radio set - the TR-9, just as in the older Spitfires.
http://www.spitfirespares.com/spitfires ... radio.html
There are lots of descriptions of contactors, but this is pretty close:-
Contactor:-
A magnetically-operated device, for repeatedly establishing and interrupting an electrical power circuit. It is usually applied to devices controlling power above 5kW, whereas the term 'relay' is ordinarily employed below 5kW. The terms are often used interchangeably.
http://www.allaboutcircuits.com/vol_4/chpt_5/2.html
http://en.wikipedia.org/wiki/Relay
http://www.allinterview.com/showanswers/75968.html
..and here is a ground-flight switch, exactly as would be used by - as Darryl has mentioned, for the Mk. V Spitfire.
http://www.spitfirespares.com/spitfires ... ical6.html
with a newer version here, common to almost all aircraft throughout the '50's and 60s, perhaps even later.:
http://cgi.ebay.co.uk/Vintage-Aircraft- ... 0730346825