Hey guy hows it going! I'm new to the site and i'm seeking help. I'm having problem with the tach on my o6 dodge cumming 2500. I did a tach test by holding the reset button down and turning on the key. Everything responed but the tach, but half way through the test the tach responed. could it be a cluster problem or cam shaft senor or what. When the truck is idling it normal runns about 500rmp and now showing 100 rpms. Looking for help and answers. Also i changed the fuel filter underneth the hood and after is when i started having the problems. Could i have hit something of did something wrong. Thanks guy look forward to your responds.