1991 Bayliner Capri 2050 5.0L Oil Pressure gauge is the only gauge working

[rmcduffie70]

My wife and I purchased a 91 bayliner capri 2050 last year, and after going through the engine/drive last summer, I am now wanting to tackle the gauges. The only gauge that works is the oil pressure gauge, however all of gauges lights do come on. The volt meter gauge shows all the way to the right, the other gauges are all the way to the left with the exception of the oil pressure that reads right at 40. I would really like to get a starting point on what I should do. Could be that all of the gauges are bad theoretically it is an old boat. I suspect something like a bad ground but I am really not sure. Any ideas?