1994 Buick Roadmaster tempature gauge isnt working

I think you replaced the wrong temp switch. One if for engine performance, the other sends a signal to the gauge in the car. It should be mounted to the engine block. I believe it is on the driver's side, lower engine area, front of exhaust manifold, mounted in engine block. Also, check under the hood, passenger side, rear engine area, end of valve cover, mounted in passenger side of engine block

Let me know what you find.