To find compatible differentials, you need to:
1. Identify your 1994 Ranger's axle: Look for markings on the differential housing itself. This will tell you the size (e.g., 7.5" or 8.8") and possibly the gear ratio. Your owner's manual might also specify this.
2. Determine if it's 2WD or 4WD: This significantly impacts compatibility.
3. Research compatible years: Once you know your axle size and drivetrain, you can research online (using forums dedicated to Ford Rangers, parts websites, etc.) to find what years of Ford Rangers used the same axle configuration. Keep in mind even within the same axle size, there can be subtle differences in mounting points or other components that might affect compatibility. Focus your search on Rangers from the same generation (1983-2011). Focus your search on years around 1994 will give the most compatible results.
In short: There's no single year that's universally compatible. You must determine your specific axle type and then research compatible years based on that information. Trying to just swap based on the year alone risks incompatibility.