P0420 Ob2 code

P0420 is not going to be plugs or wires. It points at a catalytic converter that is failing, the issue then becomes, is it really the converter or do you have a lazy O2 sensor. For that you need a scan tool to look at the fuel trims and the O2 readings as you lean and richen the fuel mix. The first step will be to look at your emissions label to determine which emissions system you have, there is the California version and the Federal version, they use different converters and exhaust systems that are not interchangeable.