Oil pressure

My oil pressure guage is not giving me a reading(below zero and doesnt move) I replaced the oil pressure sender unit and all I am getting is a flickering of the oil light on the dash board when I rev the engine ( the guage still doesnt move), I accedentally bought the wrong unit first (oil light switch) and when it was installed the guage would move to maximum when the oil light is on and then move to the below zero position when the vehicle is started(light is off) which tells me that the guage itself is connected and working. When I bought the vehicle it was working fine however it stopped working over a year now how can I get the guage to work properly again