Bought a used lexus and it was in horrible condition but mechanically great, detailed it and putting it back together I can't for the life of me figure out where this connection goes to. It has enough length to reach the connection next to the accelerator and that's it. I'm breaking my brain teying to remember but can't, any help would be appreciated.

 

That looks like the O2 sensor harness, for B2S2.

 

Sorry for the late reply, it is the b1s2 I think. O2 sensor behind the catalyst, but can't find the plug I need to get under the car and see where it comes up.
Edit, actually don't know which one it is 100% it's coming out the driver side floor panel which makes me think it goes up towards the dashboard. I'm tired and hungry and sad and I'll look into it tomorrow.

 

Bank 1 is on the passenger side, so if you tested it and think’s bank 1 then something very weird is going on…

The sensor wire comes up through the bottom pan, it has a built-in grommet on the wire at the plug end. I see a grommet in your floor pan; maybe the sensors have been deleted?

 

The sensor's wire goes thru the floor pan and this is the area where it connects on the passenger side. It shouldn't be any different on the driver's side.
Hope that helps.

 

The following discussion shows routing of the o2 sensor which may prove helpfull;

DIY IS350 Oygen Sensor replacement P0138 - Bank 1 Sensor 2
https://www.clublexus.com/forums/is-...ensor-2-a.html