You won't find a specific "power window relay" or module; the BCM itself handles the switching and control. The BCM's location in a 1995 Mustang is typically under the dashboard, on the driver's side. It's usually a fairly large, rectangular module, often secured with screws. However, accessing it can be tricky and may require partial dashboard disassembly.
Important Note: Before attempting to access or work on the BCM, disconnect the negative battery terminal to avoid electrical damage. Also, keep in mind that working with the BCM requires specialized knowledge and tools. If you're not comfortable with automotive electronics, it's best to take your Mustang to a qualified mechanic or electrician. Miswiring or improper handling of the BCM can cause significant damage to your vehicle's electrical system.