Cable dimension

Yes I see it include a relay, guess there is 12v from the locker to the relay when the "key" is on? So when you have m-unit you don't need the relay and just wire it to the lock input?

you are using the OEM key switch, so you are then only using cable in and out from the switch? Orginal there is many wires in use...?

Yeah, the M-lock sends a +12V signal to turn on the M-unit.
If you are switching something bigger(or switching a ground) you use the relay.

I just use my key switch to send 12V to the m-unit.
The wires are already there so it's not a big deal.
If I were wiring a key switch from scratch, I would need only 2 wires.
The M-lock needs 3.
 

I have started to draft the eletrical diagram and can see there is need for some fuse holders.
1. between battery and regulator, just to avoid any damage if the regulator get a shortcut. - 20A amp ?
2. between battery and M-unit. - 40 amp ?

Agree ?

Do you know about quality fuse holders I can use?