I was going to ask some questions, but solved it my self. I'll post the answers if someone else should need them.
Was looking for the database table containing the cable lines for line diagrams.
Found it: dbo.tew_line:lin_linetype; rows with 1
(Scheme wire lines seem to be lin_linetype = 0)
Then I needed to find cable relation to components (origin and destination component).
Also found it:
dbo.tew_cable:cab_id --- dbo.tew_wire:wir_cab_id
dbo.tew_wire:wir_com_idfrom --- dbo.tew_component:com_id
dbo.tew_wire:wir_com_idto --- dbo.tew_component:com_id
Keep in mind that one cable can be connected to several components, so the query often returns multiple answers.