I have a 95 3500 5.9 and the check engine light won't come on, the wait to start light doesn't come on, and of course no tach. Sometimes these things will work some times not, if they do work its only for the first few minutes. I have alreadty checked all fuses, relays, and connections. I can just barely here the computer humm when the key is in the on position but the engine isn't running. Any ideas??