Let's have a look on a shield link:
shield_link = l_fighter_shield01, HpMount, Hpxx01, Hpxx02, HpThruster02, HpShield01
0. every shield mounted on your ship, which should have an "shield effect" (capacity, regeneration) has to be in the link. If it's not, it does nothing (besides using / providing energy).
1. "l_fighter_shield01" is defining the size of the shield bubble - possibly together with the SUR of the ship
2. HpMount - not sure what it does
3. "Hpxx01, Hpxx02, HpThruster02, HpShield01" these are pssobile shield HPs
The HpThruster02 in that case is a little special - you could mount a thruster or a shield upgrade in that one (as in the Hpxx01, Hpxx02). Other mods do that with weapon HPs
4. HpShield01 - the last in the row, which effects the shield - weapon modifier AFAIK
5. if you add the HPEngine in the row, your energy will be taken away by energy_damage, when your shield is down and you are under fire
6. and you can have 2 shield_links as some found out (
as to see here