Hello all, I previously had a 2003 FZS600, silver. I'm hoping to buy another one soon (or maybe a 1000 this time 😁)

Nowhere on the internet was I able to find back side of speedo (motherboard) with wires in exact places, so if anyone has picture of their own, or can help in any way that would be very welcome

Ask and ye shall receive

https://foc-u.co.uk/index.php?topic=25376.msg29975o

If it was running then you missed something on drawing out the diagram.

The alternator has no connection to earth and the only way it knows if it is positive or negative earth is by which side of the battery is connected to the frame.
Since it is only lights and ignition it is fairly simple as lights, your relays work either way, (unless they have and internal diode but it would be written on it) and a horn with two connection. but you will have to ensure the Ignition unit is connected the correct way round.
You don't really need relays for the setup you require, just an ignition switch to turn on the power a switch to turn on the lights. a two way switch for lights,  a button for the horn and a rear brake light switch.  3 fuses should do, the lights the ignition and a battery fuse. Depending on how you wire in an ammeter if it has one and where you take the power from for the lights you may need a fuse between it and the regulator for safety

You can buy and old style two way switch with a horn button incorporated in it

thanks for looking,
I bought the bike and yes, temptation got the better of me. a squirt of easy start and a battery and it did start when I sussed out which position to have the switches in.
The wiring has not been changed since.
I will probably look into re wiring it neg earth and fitting in a key switch for security. which will mean Ive got to make new brackets, which Im also going to have to do to fit a screw on oil filter as well.