Everything matches:1989, FORD E-150, L6-4.9L, even the sensor looks exactly the same, only the new sensor has three wires and the old sensor has 4 and it is connected to 4 wires. Is there a simple trick around this?

 

You have the wrong sensor. They are plug and drive.
Those butt splices will soon cause issues. Keep them for speaker wires.

 

That is why we try to stay with OEM (Motorcraft) sensors when possible.It might be an older vehicle, but usually runs better with Motorcraft parts,, not kidding.

 

Agree, he is opening a new can of worms with those butt splices in such a harsh environment.