I have just had 2 new tires installed on my 1997 ford expedition. As i was driving home i noticed that the "Check Susp" light is on. This light has never been on before this. Could it have been something the tire installation person has done.

They probably picked the vehicle up on a lift and let the suspension hang.... Air ride suspension has a device to monitor vehicle height. They should have disabled it first... Now you have a serious problem.. Take it back to them and let them fix it.$$$$

More than likely the shop employees forgot to turn on the air suspension override switch after installing the tires.I have seen this happen many of times.Open the passenger front door and you will see where the switch is located at.It is on the right side of where your right foot normally sits.Simply switch it back to the on position and you should be good to go.On some models it is placed in the back of the vehicle by the tool storage.I hope I could help and rate me accordingly, Thanks!!