craft "add xx to lightning support"

It's a local modifier - it applies to the Damage dealt by the Wand. Spells do not use your weapon's Damage. You'd want the '+Lightning Damage Added to Spells' modifier instead.

Here is a general rule of thumb: if you had a white item, with no other modifier than that one, would it make sense for the modifier to be local? If yes, it is most likely local.

Some examples:

"Adds 10 to 20 fire damage" on a weapon.
Yes, you could add fire damage to attacks with a white weapon. Thus, local.

"Adds 10 to 20 fire damage to spells" on a weapon.
No, spells never use your weapon. This mod would not do anything if it was local, thus it is global.

"Adds 10 to 20 fire damage" on a pair of boots (lab enchant).
It does not make sense to add damage to boots. Thus this is a global mod (and will affect spells too!)



"10% increased energy shield" on a chestpiece.
The chest has an ES value which can be increased. Thus this is a local mod, and will only affect ES gained from the chestpiece. (Note, this is also the case if you craft a % increased ES on a chestpiece that has 0 base ES.)

"10% increased energy shield" on an amulet.
Unlike armor, amulets don't have any base ES to increase. This mod would not do anything if it was local. Thus this is global, and affects all ES you get from anywhere.



"10% increased physical damage" on a weapon.
A white weapon deals physical damage, which can be increased. Thus this is a local mod.

"10% increased fire damage" on a weapon.
This one is a bit tricky. If the weapon also has flat added fire damage (the first mod above), it does deal fire damage which could be increased. But here the no other modifier than this one rule comes into play. If you had a weapon with no other mod than % increased fire damage, there would be no local fire damage to increase. Thus this mod is global. (Even in the case when the weapon does actually have an added fire damage mod.)



There are a few notable exceptions.
Sometimes a modifier explicitly states that it is global or local. For example, "100% increased Global Defences" (global) from Skin of the Loyal, or "Gain Life from Leech instantly from Hits with this Weapon" (local) from Bloodseeker. In this case you should trust what the mod says.

Second, any modifier that is conditional on something else happening, for example "+0.3% Critical Strike Chance per Power Charge" on Shimmeron, is always global.

Hand of Wisdom and Action is an interesting example. Pre-3.0, it used to have a modifier "Adds 1 to 6 Lightning Damage to Attacks per 10 Intelligence". This is a conditional modifier, thus it used to be global. The damage would be added to both weapons when dualwielding. If you used two HoWAs, you would get double the bonus for every attack!

But in 3.0, the mod changed to "Adds 1 to 10 Lightning Damage to Attacks with this Weapon per 10 Intelligence". Thus this is now an explicitly local mod, and does not apply to attacks with the other weapon anymore.



This rule is not 100% foolproof, especially for some unique items, but it will work for maybe 98% of modifiers.