Yes that is the connector. It will be plugged in firmly, but the power won't be getting through to the other side.
Its one of the fat wires (White I think - it was a few years ago that I did this).
Anyway, get someone to switch the heater on / off whilst you are testing for power. That way, you'll find out which is the heater wire (obviously, with the heater on, this wire will be powered up, and when the heater is off, the wire will have no power) - sorry if I'm stating the obvious.
Anyway, once you've discovered the wire, leave the heater on and check for power in at the other end of the connector at the pin which corresponds with the discovered heater wire. You'll find there is no power there. You need to connect these two wires directly.
Just done a quick diagram (don't laugh!)... It will give you an idea of what I'm on about (hopefully):
Basically, for the heater wiring, you ar bypassing the connector