Nb: This worked for me so I cannot guarantee it will work for you. I take no responsibilty if you screw up your interior lighting.
1) Firstly the 406 visors that I got were not exactly the same as the 306 so some adaption will be needed. As you can see from the pic there is an extra bit of plastic where the wire comes out of which will not fit in the 306.
2) After a bit of fiddling and working out I ended up cutting mine and using a dremel to get it to fit into the 306. (This is by no way the only method and I suggest you work this bit out in your own way for you own satisfaction.
3) To fit the new visor I used the original front pilot hole on the 306 (furthest away from the windscreen - the bit you see) and drilled a new hole for the back. There was a gap of about 5mm so I cut a bit of the roof lining from the centre light console to fit. Its not great but its the best I could do. (Probably the only downfall to the whole fitting)
4)So now you've got this
5) Now for the wiring. Disconnect your battery.
6) As I had also acquired an auto dim mirror, connections to one of the lighting terminals were already taken up, so not to overload this terminal I had to find somewhere else. So I decided to connect the visors to the door open warning light.
7) You will notice both visors have 2 wires, 1 red and 1 blue making in total 4 wires. I decided to connect the new visors together instead of seperately. Spliced both red and blue, connected - making 2 wires and used terminals to bring it all together. With a spare bit of wire I had lying around coming out the other end.
8) Now to find the right terminals to get the visors to work properly.
9) As you pull the plug out from the door open warning socket you will see 4 wires, 1 red, 1 white, 1 yellow and 1 green/yellow (earth).
10) After a bit of trial and error the red wire from the visors needs to be connected to the earth and the blue wire from the visors needs to be connected to the white. Obviously your connections will be much cleaner than this as you know which terminals need to go where.
11) Once connected you will need to test that everything still works as it should do.
12) This connection makes the vanity lights come on without the ignition on
13) And both lights on without any dimming