I have a 1976 l48 and the tach is always at zero and doesn't pick up. The oil pressure gauge works and reads well, in between 40 and 80. The issue I'm having is that sometimes the oil pressure gauge will stick itself all the way to high and won't come off unless I shut the engine off and immediately turn it back on. Occasionally the tach picks itself up to 5 and stays there when this happens. Could it be a bad sender? Or maybe a ground issue?