I saw this question on BGG , and was surprised by the answer someone gave. The question was whether Ardus could use the surge ability on Master-Crafted Weapons if Master-Crafted Weapons were equipped to an ally within range 1-3. My knee-jerk reaction was "no," but I couldn't find a way to disprove it in the rules. To the contrary, I found this rule:

88.1: "Upgrade cards grant additional effects to the units that have them equipped."

So does this mean that the surge ability of Master-Crafted Weapons becomes a surge ability of the unit it is equipped to? If so, then Ardus would absolutely be able to utilize surge abilities on upgrade cards attached to allied units.

That's how I interpreted it. Master-Crafted Weapons give the unit and additional surge ability. Wind Rune gives the unit an additional skill action.

If that wasn't the case you'd never be able to actually trigger skills that weren't native to the unit.

RRG, pg. 17:
'Skill is an action. When a unit performs a skill action, it chooses and resolves one of its abilities that has a skill icon.'