I bought a cheap tach on line and am looking for anyone that can tell me for sure how to get it to work. I have id the plugs at the coils i have tried the adaptor with the resistors and diodes and get no reading at all. i made a y cable with no resistors or diodes and get readings but sometimes the coils cross fire making it run bad or die at the lights and possibly dropped my fuel range 20 miles per tank. can you tell me for sure how to make this work or did i by a expensive hood ornament