Thanks once again. I adjusted the height of the PU's and that seems to solve the problem of difference in output.
The first problem (mid position not working) was indeed as you said: volume of bridge should be open.
I'm still encountering some issues though.
1/When turning the volume of the neck PU up, the bridge PU sounds louder and vica verse
And some other weird things: turning bridge all the way up and neck all the way up: i hear no sound, turning bridge a little bit down, there is sound
I used braided shield wire to connect the pots to the toggle ( https://www.gitaarupgrade.nl/webshop...son-style.html) Was that stupid?
would that cause this problem?
2/ I have the feeling serial/split/paralel isn't working on all pu's. Where would I have to hold my multimeter to see if it's working as planned?