I am working on a 1993 Explorer with the 4.0 V6 Engine. I am replacing both the upstream and downstream O2 sensors due to codes. I didn't have any trouble removing or installing the O2 sensors, However, When I ordered the O2 sensors, They sent me Delphi ES20064 sensors with original style plugs. The only problem I have I this. I would have to be a magician to be able to unplug and plug the new sensor in. Consequently, I must splice the wires. My new 4 wire Delphi has the following colored wires. Black, White, Purple and grey. The Bosch I removed, had a black, 2 whites and a grey. On he Delphi, the heater wires I believe, are the purple and white wires which I had planned on splicing to the two Bosch wires.
My question is this. Are the two white wires (heater circuit) polarity sensitive?

I would stop what you are doing and get exact fit Motorcraft oxygen sensors. Oxygen sensors are extremely sensitive and splicing wires will likely result in codes being thrown.