There generally is a plastic holder the retains the speedometer cable under the hood that is attached to a small metal bracket near the back of the engine/front of the transmission on the left side of the car. Squeeze the back of the plastic holder with your fingers and the plastic holder will come lose from the metal bracket. This will give you a couple more inches of slack in the speedometer cable which makes it easier to disconnect and reconnect the cable to the back of the speedometer. When finished simply reattach the plastic cable holder under the hood.

Using a wire coat hanger wire about 8" long create a hook on the end on the wire. Push the hooked end of the wire between the dash opening and the instrument cluster on the left and right end alternatively. Using a pair of vice grips on the straight end of the wire you will be able to gently pull the instrument cluster out far enough to reach your hand behind and disconnect the speedometer cable. The instrument cluster will then pull out even farther to give you access to disconnect the wires and the oil pressure gauge line.