I have the FFR set of 6 gauges that came with a coupe kit. The oil pressure gauge is installed in another car I am building and has started acting irregularly. The gauge goes directly to 100 pounds when started even though it previously worked fine, and stays pinned at 100. I installed an additional mechanical gauge and it shows what I believe is the correct pressure readings for the engine. My question is where do I start to find the problem? Is there a way to test either the sending unit or the gauge itself? Thanks for any suggestions.