Fuel fuel pump relay?

So, after a 9 year pause after getting the 1991 Mustang 95% complete with the new 393W build, I am getting around to finishing it. I got it to where it would crank, but the fuel pump wasnt coming on. By just putting power manually directly to the fuel pump plug at the tank, it pumped fuel to the motor, and it fired up. Now to figure out why the fuel pump isnt getting power. So, some back story:

It was a 4cyl car. I rebuilt the entire car from being gutted and on a rotisserie, to a complete car where everything is new inside and out. I remember buying a 1991 5.0 harness and putting it in there with the correct A9L computer. So, Im thinking maybe I didnt plug in the fuel pump relay under the drivers seat, so I pull the seat and look. The fuel pump relay wiring is there, but there is no relay. The thing that I'm lost on, is that the wiring socket was plugged into a black plastic cover with a factory part number on it, so obviously theres never been a relay plugged in to the relay plug.

So, my question is....did the 4cyl cars not use the fuel pump relay? I don't have a relay handy I can just pop in there and try. I thought I'd ask you guys first. I only changed out the engine harness, so the body harness is still the 4cyl wiring. Theres only the one relay under the MAF unit, so I dont think I somehow ended up with a 92-93 harness. I've been out of the loop with the car hobby and this car for several years, so maybe I overlooked something.

BTW, it sounds awesome!