I'm having some issues with the tachometer I just tied to hook up today. There was the 4 wires coming off of it, +, ground, illumination and the one that goes to the coil. First off the light inside the tach didn't work, no biggie. I go to start the truck, it starts up , but the tach doesn't work. I grabbed my test light and I have power going to the tach. The wire going to the coil is sending juice to it, but when i put the test light on it, it lit up and flashed with the rpms while the engine died? Not to sure if I hooked it up wrong or what any ideas for things to check?