TNGChris

I'm not sure what else you need?The IAT input is at C5 on the ECU.It receives 5V from a common output(I'd have to look at a schematic to see which one),but if there's an issue with that supply,other sensors would also be offline.The sensor itself is not polarity sensitive,and has 5V applied to one side,and an output voltage on the other side.The shop manual will have a range of allowable output voltages for various ambient temperratures.
1-Using a multimeter check to see if there is 5V at the sensor plug with the key in the ON position.If not,trace the wire back to look for shorts or open.
2-check the output wire right off the sensor using a multimeter.It should correspond to the chart of allowable ranges(buy a cheap shop manual,search the netz to find that range of output.....or I'll find that too if needed).If there's no output at all check the connector pins for good contact and check the sensor for continuity across it's pins(replace sensor if open).If there is output but not in line with the allowable range,replace sensor.
3-If output is correct,check pin C5 at the ECU to see if you get the same reading you got right at the sensor.If not,check wiring between the two for shorts or open.If so,make sure the ECU pin looks good and is making a good connection to the ECU.

One of these things is your problem(you said you've already made sure you have the correct plug connected to the IAT).Figure out which it is.

ALL of this is outlined in a shop manual,which you absolutely should have if you're working on your car.Even a $15 shitty manual from an auto parts store will have the basic procedures(like this)in it.Ideally you want a factory Helm manual,and the $70(or about half that used on Ebay,or $5 for a copy on disc off Ebay)is 100% worth it.The Helm will help you diagnose and fix ANY issue you'll have with your car.You'll no longer have to rely on idiots on forums giving you wrong info.

Fabrik8

You can pretty easily find a PDF copy of the Helms manual if you poke around a little bit.