This holds true whether the ship’s secondary weapon(s) have an equal minFireArc and maxFireArc defined or if it is left blank to default to forward-facing.

EDIT: See comment below.

assumedpseudonym 9 Jul 2016:

 Scratch that, I was looking at my code wrong. What’s actually happening is that AI ships won’t fire weapons with linkedFire="always" if no other primary weapons are installed. The former functionality was that in the case of multiple primary weapons where all of them were set to linkedFire="always", the first listed was used as the ship’s primary weapon. I have not checked the behavior of linkedFire="whenInFireArc" as yet (and don’t currently plan to, admittedly).
 It’s less of an issue than I originally thought it was, but it could break pre-1.7a2 mods that were written without the current functionality of linkedFire in mind. I’ve changed the title of the ticket and am leaving it open, but I’ve made the necessary changes to my own mods already and won’t grump if this gets resolved with no action taken.

george moromisato 26 Jul 2016:

Basically, the code first computes a firing solution for its primary weapon, and then and only then, fires any linked-fire weapons. If there is no primary weapon, then there is no firing solution—I guess that's the definition of primary.

I will resolve this with no action taken, but feel free to re-open in the future if there are issues.

Thanks!