o2 sensor in manifold where does it hook up at on a 85 2.6 liter caravan?

I bought a 85 mini ram van (cargo version of the caravan). someone has changed the motor in it at some point and missed hooking up the temp sensor, fuel pump hoses where on backwards, and the o2 sensor.

I have all of them fixed except for the o2 sensor there is just a little piece of wire hanging off of it (black) and i have no idea where it is suposed to be hooked up at. there is a gray wire running down to the vicinity of the o2 sensor but i am not sure if it is the right one or not.

The van runs great but when it warms up it has difficulty staying running.

any help i can get getting with this will be greatly appreciated.

Thanks!