check engine light

How much does the check engine light affect the car's performance? I have just installed a set of bbk longtube headers on my automatic 94 mustang gt. When I bought the headers, I didn't know that it was for manual trans only. So I made it fit,also I bought o/r h pipe. I have only one 02 sensor working right now. The other can't clear because if can't clear the auto trans case.

Is it possible to splice into my o2 sensor on the driverside and connect it with my the one on my passenger side. This is to compensate for the missing o2 sensor on the passenger side because the sensor can't clear the underside of the trans. Will this fool the ECU? Also, I've heard of people wrapping the sensor with foil so that it doesn't heat up and send the signal. Do you think this is a good solution. I know that without the signals from the sensor the ecu will run in an open loop circuit.