service engine light

I've got a '90 Lesabre with just over 42,000 miles. I put a new computer in it, because it would repeatedly die on the road. Now, the service engine light stays on. Before the new computer was installed no lights came on at all. I had a my mechanic check it with a code reader. It came up as a faulty Oxygen Sensor. So we put in a new one along with a second and no change. The engine light still stays on and you can smell the richness in the exhaust, but the car runs great anyway.

How are the wires going to the O2 sensor(s)?