As Adsum said, it was on Lewis' Arcade. It also had an entrance on Piccadilly (Mosley Street).
On Youtube you can watch the film Hell Is A City. In the opening shots through Piccadilly you pass through the bus station and you can see the sign H. Wiles on Mosley Street. Also in the closing scenes Stanley Baker walks through Lewis' Arcade with Wiles window in the background. I should also mention there is a rare shot of a famous pub - The Fatted Calf - in the film they changed the name and location. Alas, as a young under-aged drinker I missed this landmark, tucked away on Compton Court. I only just missed it though as I called in Seftons which was just around the corner. You can find all the pics on Manchester Library Archive. There are about four pics of Wiles, one way back when it was a chemist.