EASA part 66 BBS on www.EASA66.org gives you hints to get the licence!- Many Free PDF - New Info continuously added!

BBS EASA66 -> Free Moodle LMS on www.EASA66.org/moodle
https://easa66.org/BBS/

Modules 11 &13 Airplane and Avionics Info

https://easa66.org/BBS/viewtopic.php?t=132