Just to elaborate on Jim's explanation a bit...

Get a flashlight or a drop light, and on your back, stick yer head under the dash on the driver side. Look at the back of the speedo pod, you should be able to see a small square black "slide" switch. As Jim said, move it to the opposite position. That's all there is to it for another 90K miles.

C/YA!
Jeff
'88 Trooper
2DR LWB 4ZE1 5SP
bone stock DD