On an '88 SR5 4x4 with 22RE I have just replaced the O2 sensor with a Denso unit that I bought on eBay instead of from Toyota. It came without a grommet for the gaping hole under the driver's seat. Is there a preferred way to plug that before fording rivers, or splashing through puddles anyhow?

 

O2 sensors, even dealer supplied ones, do not come with that grommet. You will need to order a new one from the dealer.

 

I have the old grommet in decent condition still on the old sensor wires. I could easily snip the wires and take it off, but then forcing the new connector through the grommet's aperture would be like a gerbil giving birth to a hippopotamus.

I was thinking of resorting to a gob of silicone sealer unless someone comes up with a better way.

 

When I bought my 02 sensor from Toyota is came with a new grommet ready to go...

 

Later models have the connection that does not go through the floor board. So I guess it depends on what year you have...

 

Finally figured it out. You can unclip each terminal pin from the connector body with a probe-type tool. Then pass just the four wires through the center of the old grommet and reassemble the connector.

Obviously you need to keep careful track of which individual wire goes where.