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.