These things can be frustrating , but the dash wiring was not, in my opinion, designed to be out in the weather for 50 years, that being said, any movement or handling of the wires can cause disconnections or faults and I wouldn't be upset at the installer for this happening. If they fried a bunch of wires then I would have issue. It wouldn't hurt to remove the cluster and give all of the contacts a good cleaning. be carefull not to damage any traces, I would use a pencil eraser to cleanup around the lights and the studs.