Huh? As far as I can remember, in 2E anyway, if you were a multiclass Fighter/Magic User, you could not cast wizard spells (arcane spells) in metal armors save for elven chain. At least in 3E you had the chance to cast in metal armor, you just have Arcane Spell Failure. In 2E, the answer to casting arcane spells in metal armor was simply "NO!"
Please correct me if I am wrong. It's been a long time since I played 2E and even longer since I played 1E. But if they DID have a way for magic users to cast in metal armor, I'd like to be reminded of it.