Classic Wireing door mirrors

My 88 classic has lecky door mirrors for adjustment and heating, problem being when I bought it the control switch for the adjustment was missing, normally sits in the dash fascia next to steering wheel.
After searching for a year I managed to get a switch off ebay but I'm still looking for the link lead that connects to the part of the loom that goes to the mirrors.
While doing other jobs, most recently new clutch master, I have been trying to identify the connector block on the loom and at long last think I have narrowed it down.
So to my real question, if I use a bit of light cable, perhaps with a fuse inline, and try it in various holes in the connector block to try and make the mirrors work, whats the worst that can happen? what I really want to do is find out what wire does what and then I might be able to make up my own link lead to the switch. Obviously I will need an earth as well.

edited to say I think the link lead from switch to loom is PRC6906, really seem to be like rocking horse doo doo nowadays, so thinking to make my own.

Not a lot, blow the fuse is very possible, relative simple, make a note of the wire colour and the direction of the class movement.
Following a wiring diagram in (Haynes RR to 1990) is always the best bet, only understand was is expected to happen when a 12v live is applied to a specific wire.
So it up, down, left and right, and the earth for the glass, the heater is just 12v taken from the rear screen circuit, u already have the earth at the mirror.

You could try the disco1 switch for additional fun as it is similar in its function.

Hey, thanks for that, didn't realise the mirror acted as an earth so that at least is one wire out of the way.
I have the brooklands manual but to be quite honest following a circuit diagram for me is like trying to decipher the mad wanderings of a spider thats fallen in the inkwell.
I'll have a bit of a play once the weather warms up a bit.