Wiring Queries

The first black wire sounds like the reverse switch, for the box.
The multi coloured male one will plug around the wiper motor area.
Anything green with red is the headlight jungle.

Throw the Gregory's Escort manual diagram away with the RS.

I have a great auto sparky on Bribie that knows his stuff.
You can waste some time with the spaghetti.

Escort shop owner Phil is also great with Escort wiring.

when i was rebuilding my mk 1 cortina i left the electrics to the experts as i was informed by the Auto electrican that if i had joined these 2 particular wires together she would have gone up in smoke and 5 yrs of work down the drain my advice call in the experts if need be

According to the Ford factory repair manual( I also checked my car's connections too) the wiring for the interior light should be a white wire with an orange stripe for battery & black wires from each of the door switches.
For the heater, the male connector(black wire with the red & yellow stripes) which comes from the heater fan should connect to a light green wire with a light blue stripe(with matching female connector, of course) from the loom. The three spade connections for the heater series resistor should consist of one brown wire(from the heater fan motor) & the other two run from the terminals on the dash fan switch, which should be one red wire with a grey stripe & one orange wire with a black stripe coming from the loom.
This is assuming your loom is a late 1979 or newer one though, as Ford revised the wiring in late '79 & some wire colours(among other things) differ from earlier looms, which the gregory's seems to have missed by the sounds of it, as the "brown/white & brown/yellow" wires you mentioned would be correct for an earlier mk2 escort loom.
Good luck, sounds like you're nearly there too!

Yeah, the 'Gregorys' for my BF2 Fairmont is a bit scant on detail too, to say the least!

A Violet wire with a white stripe should be for your rear demister. Runs from the dash switch to the relay & then on down the loom to the rear screen. . .in theory anyway. . .the joys of thirty year old wiring eh?