I have an 1998 Expedition that is having some for wheel drive trouble. There is a switch near the steering wheel on the dash that has options for 2 wheel drive, 2 wheel alternate 4 wheel drive, 4 wheel high, and 4 wheel low modes. When I try to switch it it doesnt seem to engage the 4 wheel drive. Sometimes I can get the 4 wheel low to work but then it doesnt want to come out of it. The guage panel will say its in 4 wheel when i put it in however the light sometimes jumps around to 2 wheel and 2x4 etc. Is it the switch or the drivetrain that is messed up?