oil preasurre gauge

[littlboo1]

i just purchased a 82 wagon from my brother and the oil preasur gauge is reading all the way over, got to checking someone has put a sending unit for lights instead of one for the gauges and have wired a double pole
plug from somewhere and am wanting to change it but am having a problem figuring out which wire should be on the one pole unit any help
would be appreciated

thanks for your time

littlboo1