A friend of mine bought this house a while back, but now he is actually going to live in it himself he thought it best to make the wiring safe, so he ripped out all the original wiring and has started rewiring it all, all the new wire he has color coded with tape so he actually knows what cable is for what, yes you may have guessed by that last sentence he is not a Thai.
There are generally 2 ways to do your cable runs, on top of the rendered finish which is the normal ugly way where you get to see the ugly cables for the rest of your life, or inside the wall, by rights the cables inside the walls should be run in yellow conduit, this sometimes allows you to pull through damaged cables to replace them, but a lot of the time they get jammed as the cable aint flexible enough, also if your drilling a hole and yellow plastic starts coming out you know you have hit a electric run, trouble is as most of the time percussion drills are used the odds are you gonna hit the cable as you see the yellow come out, percussion drills are a lot more powerful than your run of the mill hammer drills.
Now as this house is already built it means cutting out channels in the render with an angle grinder and then chipping it out, if you actually live in the house at this time it is probably best if you go out for the day while they are doing this, it is noisey and will cover your house in cement dust, and no, they wont clean up the mess properly so you will be finding dust for weeks to come, and if you have a maid there is a good chance she will resign if this is gonna be a big job.
Anyway with this first picture you can see the channeling is nearly complete, this is for the kitchen lighting, for lighting you just need to use 1.5mm electric cable, you can use 1mm cable theoretically but why bother.
As conduit isn't being used you have to jam that cable in the channel, this can be done by cementing it in every meter or so just to initially hold it in before you render it off, or small masonry nails to hold it in place, or even old bits of concrete jammed in there, now this aint really the proper way to do it and it is much better to use conduit, but I am just showing you how Thais may do it in your house.
This next picture is of a mains run for some plugs, as you can see there is an extra cable which is being used for the earth run, as it is mains this is 2.5mm electric cable, in theory you can use 2mm cable but I don't think Thai planners take into consideration how many electrical appliances the average farang has and uses.
Once the cement is dry you will see that it stands out from the original render on the wall, ie sticks out a bit, has cracks in it because they let it dry off too quick, and also the texture will be different to the rest of the wall as the sand size and ratio on mixing will be different to the original rendering, the only thing that helps to any degree is to go over it with a very thin coat of plaster and then give it a quick sand down, this will look better but then it will be a lot smoother than the rest of your wall so still stands out if your looking for it.