How do you hook up an A/F ratio gauge?
Also, is it worth hooking it up with a stock O2 sensor?

You wire it to a O2 sensor.....nothing fancy.

To me it's completely not worth it with the stock NB O2 sensor. At part throttle the light will just flicker back and forth. At WOT the NB O2 is not accurate enough to even get you close to what AFR you are actually running.

What O2 sensor is a good one to put in a 305 V8 TBI?

All an a/f gauge will do is show you a nice light show. You don't need one unless you want to get into some serious tuning. See, a narrowband o2 sensor (what the stock sensor is) only outputs a 0-1 volt signal. It is inaccurate and useless. What you need to do is buy a wideband setup that will output a 0-5 volt signal. This will give you very accurate readings. The cheapest solutions include the Innovate LC-1 (with the XD-16 gauge), the AEM UEGO, or the PLX M300.

Accurate and inaccurate really isn't the best way to describe the stock sensor to the WB. They are just designed to do two seperate things. As the name implies the NB or narrow band only senses 14.7 to 1, it will indicate richer or leaner than that but it is NOT accurate at sensing any other AFR other than 14.7 As the name impies a WB or wide band has the ability to see all AFR's between 10 and 20. This is very handy for tuning, but not really in guage form. When you are making a WOT run it's difficult and dangerous to be watching a guage closely. What most guys do is log the output from the WB along with all the other sensor readings so they can make an educated decision on what to change in the chip to correct the tune. This is all done after the fact on the side of the road after making a WOT pass.

In my opinion you really don't need to know what the AFR is unless you can change it by tuning the chip.

Not to nitpick, but a NB o2 sensor does not sense 14.7:1 per say...
It senses stoich.
Say you switch from regular gasoline to gasoline with 10% ethanol blended. Now stoich is about 14.1:1, and your NB o2 sensor now senses 14.1:1. Now say you switch to E85 (85% ethanol 15% gas), now your NB is reading about 9.7:1, which is stoich for that fuel.

If you look in jegs you can buy an autometer guage for around 60 bucks then get the O2 sensor kit from them for 94 bucks. still pricey but cheaper then all the other ones.

The cheap guages still use a NB sensor and have all the problems associated with them.

The cheapest "sensor" out there right now is around 200 dollars and does not come with a guage. You are looking at over $300 for a WB based guage.

Discustu: I've never heard your theory of NB operation, not to doubt but where did you get your information?

I'm not exactly where I know that from, but it's been my understanding for quite a while now. Maybe wikipedia?
A NB o2 sensor measures the oxygen content of the exhaust gases, relative to the oxygen content of atmospheric air.
Therefore, when you have a stoichiometric condition, regardless of what fuel you are using (or what ratio stoich is for that fuel), there will be the ideal ratio of oxygen in the exhaust gases to produce .45V.

Ever wondered why you had a slight lean condition when you switched to 10% ethanol blended fuel? I did. Mine went from right around 128 to about 134-135 with the fuel switch. It's because the ethanol fuel only required 14.1 parts oxygen, rather then 14.7, so there was about 5% extra oxygen left over.

Since the O2 only senses oxygen content, it has no way of knowing what the AFR is. The final O2 content can be used to get an approximation of stoich, and the lambda (unitless ratio of the current AFR to stoich) thats derived from the O2 content can be used to estimate the AFR relative to stoich for the fuel in use (~14.1 for most blends today). The stock O2 only really senses stoich, rich, and lean. The output is very steep to either side of stioch, so its of little use for determining the AFR.