99-04 Mustang GT: Which heater core hose is the inlet?

Don't know offhand, but you can start the car, and feel the hoses, and whichever one is the hotter of the 2 would be the inlet. If you can't tell a difference, turn the heater on full blast, this will cool the coolant in the core faster, so you should definately be able to feel a difference in hose temperature.

If I recall, it's the drivers side hose on foxbody's.. probably the same on these. Good luck.