1996 Geo Tracker lighting issue

I recently had a hitch installed on my 1996 tracker. The shop did a great job, however I now have no running lights nor brake lights nor instrument panel lights. They don't know why. When I took it to them the lights all worked. They worked on the car with the battery disconnected.

I have checked the fuses, the bulbs, and the relay. All are working. The relay works because the only light coming on is the ash tray light. I tested and replaced each fuse just to be sure and no results. They dropped the gas tank to do the welding and re-installed it. Is is possible they missed a wiring harness connection? They say no, the only harness connection was to the tank float. It is baffling to me. I am an electrician so I do know what I am looking for and how to check it. It just seems to me that something is missing. I do not get any signal in the parking and side lights, and no brake lights, and no instrument panel lights.

When I bought this car I had a similar problem but immediately found a bad fuse. After that I never had an issue. Now I can't begin to connect the trailer lights due to this new issue.

Can you please help me? This is a business vehicle and lights are certainly important.

Thank you very much.