which wire?
if it's the wire from the ignition switch, check the "volt" bulb in the dash. it should be on with the key on and engine off.
before you take anything apart, push in on the gauge cluster with the key on and see if the light comes on, if it does, you should pull the cluster out and clean the contacts.
if it doesn't come on, pull the bezel off and use a needle nose pliers to gently wiggle the bulb to see if it's not making good contact. if it still doesn't work, change the bulb.
