How do you start a series 2a heater?

I have owned a series3, a Defender, 3 Disco's and a Range Rover. I have lived thirty years under and over Landies, but cannot get my "new" series 2a flat smiths heater to jump into action. I think the previous owner plumbed a series 3 matrix onto the flat one, but the pipework still goes through a plumbers tap! There is a heater knob. Slow, fast and something else that has rubbed off. Is this the switch? I cant find anything else, so I tried pulling it (nought). There is a wire going to the fan underneath the passenger footwell. I checked, but no power when the switch is turned. There is a coil of wire behind the instrument panel. I think it may be from a diesel, but couldn't be sure. Any ideas, I need something to get these windows defrosted?

Thanks