What gauge wire would I need to use on these guys?

I know you need to extend the harness from the engine not the sensor.

I'm also going to solder and heat shrink the wires but I don't know what guage to go with.

Any help/ideas apprecitated.

 

I just replaced my O2's to the heated variety so I had to extend the existing wiring as well as add wiring for the "heat". I wanted mine to look factory so I bought both the new O2 sensors which have a four wire male plug. I also bought the female portion so that I wouldn't have to solder them on every time I replaced O2 sensors. At any rate I got the female plugs from Jason Cromer for about $15.00 a piece and they came with about 18" of wire and crimp type connectors included. If this is a long enough extension for you I would go that route. They are factory AC Delco parts and I just crimped them on, wrapped them with electrical tape and stuffed them in some convoluted tubing. I've had them on now for about a month and they work perfect. BTW if the wire is 18 guage.