RE "extra" black wire to refrigerator:

My van is garaged at my shop some distance away, and my log book and notes
are there too, so I offer this from memory. It's been a year since I had my
fridge out for a major overhaul, and if I am remembering correctly, the
three-wire connector consists of:
1. 12v only on when the engine is on and the alternator is producing power;
this is accomplished by the so-called fridge relay under the driver's seat.
2. 12v always on, which supplies power to the refrigerator condenser fan,
which must be available to cool the condenser not just when the fridge is
operating on 12v, but also when the fridge is operating on 120v as well as
propane.  In actuality, the condenser fan can come on even when the fridge
is not in use in any mode; a high-enough ambient temperature inside the van
will cause the thermoswitch on the condenser coil to close, turning on the
fan.  The ignition module for electronic gas ignition on the later Dometics
is also powered from this always-on source.
3. Ground

As I recall, the stand-alone black wire is energized when the thermocouple
produces a current in the presence of a flame in the combustion chamber,
and is connected to the LED panel; the lowest of the four LEDs on the left
of the LED panel(when there are four)is thus illuminated to indicate
successful operation on propane (sometimes hard to see in strong daylight).

Bill