I recently had the head off to fix a burned valve. I've got one connector I can't figure out what this plugs into.

It's on the same leg as the lower 02 sensor and the pressure sensor for the turbo.

Can someone point me in the right direction?

Looks like 3 conductors

 

There's also an Aux Coolant Pump on that same leg, located just below the oil cooler / filter housing. If that's not it, try starting the engine and see what codes come up.