1. ask moderators to move this topic to the mods section
2. SPOILER ALERT DO NOT READ BELOW IF YOU HAVEN"T PLAYED THE GAME AT LEAST ONCE
3..if you have FIXT installed on the Fo1 engine then only way to give him armor is through "change armor" option
( please be noted that Ian is already wearing leather jacket when you meet him [and no it's not visible via inventory or armor slot in control party members mode] and the only way for him to change armor is to give him some different armor [other than leather jacket] just by giving him leather jacket from vault 15 into his inventory is not going to cause the option to show up. You need at least leather armor for that and the closest one to have is by killing off raiders after rescuing tandi next give it to him by starting conversation trading the armor to him and going back to conversation a "change armor" or "change your armor" etc. option should show up somwhere in the indepth dialog. if you click it finish the conversation and ian should change his armor (that is if You've picked the option to change armor during FIXT installation)