Should I have to pay a diagnostic charge bill?

The tail light circuit in my car kept shorting, so I brought it to the dealer and had them run diagnostics for two hours, and still, they couldn't figure it out. They said they had their best mechanic working on it (40+ years) and to come back the next day since they were closing. I went home and tried unplugging my stereo and replacing the fuse, which fixed the problem in 5 minutes. In addition, my remote starter no longer works. It was fine before they messed with the wiring. The seat belt and overdrive lights also start to blink randomly now. Would this be a legitimate argument for small claims court? They were supposed to diagnose the problem and fix it instead of making things worse. I've also heard wiring problems can't be diagnosed by hooking it up to the computer. This all takes place in Connecticut.