See picture below. Engine light came on. Popped the hood and it’s leaking from this black piece. See picture below.

 

better picture.

it’s leaking when the car is running.

 

That is the oil pressure sending unit (low pressure switch). Your setup has a mechanical gauge and a T with the sending unit (switch) for the OIL warning light in the dash.

Is it leaking around the threads? If so, remove and wrap with Teflon tape, reinstall, and see if it still leaks.
If it's leaking around the 1/8" plastic line, the brass ferrule may be loose, and slightly tightening the ferrule nut to tighten it a bit more may stop the leak.

edit:
I re-read and saw the engine light came on - do you mean the OIL light? If so, I doubt leaking threads would do that, and the switch itself may be bad and need to be replaced.

 

The photos make it difficult to tell exactly were the leak is. The switch with the wire is the factory low oil pressure switch that operates the OIL idiot light. The rest of it was added by a prior owner to allow an aftermarket mechanical oil pressure gauge to be connected while retaining the OIL idiot light (that's actually a smart thing to do, by the way). The fitting for the pressure gauge tube has oil around it also, which implies that it is leaking.

 

I always set mine up with the idiot and mechanical gauge except I hook up that sender pointing straight up and the braided oil line to the mechanical gauge. They do fail from time to time. What was your oil pressure gauge reading at the time?

 

You're leaking everywhere, including the temp sender and the thermostat housing. Replace the oil light sender, clean and use thread sealant it on all the other connections.

 

Thanks for all the replies. It was leaking around the black plastic piece. I bought a new one for about $15.00 and put it on. The light is no longer on and no more leaks.