Wiring problems of the 1999 Infiniti QX4

Consumer stated O2 sensor was causing check engine light to come on and stay on. This has been going on for the last 6 months. Consumer took the vehicle to the mechanic, and was subjected to having a wiring harness installed. Consumer had that done, but it did not solve the problem. They were talking about another $1200. 00 to repair something else.