You probably did the same thing I did.....left the 3.4L oil pressure sending unit in and burned out your oil pressure dash gauge. I was able to get mine to work a little....which is to say the needle moves a little, but that's about it.
The two sending units (and therefore gauges) work differently. The 3.4L sending unit will send a full 12 volts to the gauge and that will cause the needle to go all the way right and bend a thin metal strip in the gauge. Once it's bent the gauge is pretty much gone.
I've heard of a one guy who had some success in re-bending the strip, but I failed.
'93 4Runner - 3.4L 5VZ-FE, 2" body lift, on-board-air system, custom gauge cluster, rear e-locker, electric fan, custom built front and rear bumpers, sliders, 4,88 gears...all on 33x12.5's.