That heater coil/spring looks the same as on my Sanyos. It might be controlled by the controller board.
My heaters were traceable back to a relay on the main controller board. When it's warm out, the heater stays off..
I would keep the controller if possible, since it might have a good defrost setup.
When you hook up AC power (to 5&6), two of the other terminals should go hot, to power the indoor unit.
You could find them with a voltmeter.
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If you have found the 2 power lines, you should find out if one of the low voltage lines is ground.
For safety, one one of the lines going inside the house
might be ground.
If it is ground, that only leaves 1 line left for control.
Single line controllers sometimes use a DC bias voltage and the control input is a set of resistive loads.
Maybe like this:
A. Zero ohms (short) = standby
B. 2.3V+ = Cool (medium resistance)
C. 5.0V+ = Heat (high resistance)
D. No load = Maintenance mode, use test button.
If were to find one of the lines had low voltage DC on it,
you could try connecting a Pot or variable resistor and turn it's resistances up and down to see if it changed the operating mode..?.
The other side of the pot would be connected to ground.
But, before I did this, I would do a lot of searching for a schematic diagram.
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If there is no ground, and you have two control lines, one
might be compressor ON and the other one would be mode, cool or heat..
Hopefully both these lines would have a low DC voltage on them..
