o2 sensor help!

[FstAsVR4]

I am completing my 16g build and have many unused plugs, I am trying to find out where and how my o2 sensors plug in. I have two plugs up front down by the thermostat housing and no idea where the rear ones are. Can someone please help me out on where to locate the plugs. Also my gas gauge doesn't seem to be working it's on empty but the light doesn't come on. Thanks

[DocWalt]

One of the rear O2 plugs (upstream, before precat) is on the front fuel injector harness, I don't know where the other one is, sorry.

There's two sensors in the tank, one that turns the low fuel light on, the other does the gauge. The one for the light might be disconnected in the rear (broken wire, whatever) or stuck internally.

[FstAsVR4]

Ok I saw the one on the fuel injector harness but it barely fits, it's been over a year since driving my car so I don't remember how anything was. And thanks for the info on the fuel gauge.

[DocWalt]

Weird, I had embedded a stealth316 picture in my post, but it disappeared...

[x2xtreme360]

The rear o2 sensor (primary) is located right on the front fuel rail. The bolt on the right actually holds down the connector for it. The o2 sensor then goes to the rear precat.

The front o2 sensor connector is located right by the alternator.

The secondary o2 sensor plugs (if you're 94-99) branch off the engine harness right after all the coolant temp sensors (I'm assuming this was what you meant by thermostat) and there's 2 plugs with four wires each. The complete they very end of the harness down there.