1991 Heater / Cooling issues after engine repair

My next door neighbor took a trip this past weekend and his car died while he was out of state. As it turned out the Coolant Temperature Sensor (CTS) that supplies temperature signals to the Engine Controller Module had died, which at the time he did not know. He had the card towed to a garage and the garage diagnosed the problem and fixed it. When he brought the car back he discovered that the over-temperatue indicator no longer lights when the ignition switch is turned on. Also the temerature indicator no longer works, and there is no heat coming from the heater now. These all worked prior to the repair job. Additionally, the fan motor does work. I just now talked with my neighbor and he said that "Jiggled" some of the wires under the dash and he got the heat and the Over-temperature indicator to work but that it was intermttent and that the Temprature Gauge still did not work. Then all three were not working again. We have tried to diganose this problem with the Chilton repair manual but the schematics are virtually useless for this kind of troubleshooting. It seems like there is at least one open or intermittent ground going to the instrument panel harness. Does anyone have any ideas of what or where to look for the problem? To me it seems like something that was removed for the diagnostics for the CTS was not reconnected or is making a bad connection at best. Any thoughts regarding this problem would be greatly appreciated!