I HAVE A 1978 f600 FLAT BED SIX WHEEL DUMP. I put in a new tachometer because I could not tell how high rpm the 330cid v8 motor was turning when traveling the highway. I never touched or moved anything dealing with the signal or emergency flashing lights. since I iunstalled the tach those lights do not work. I checked the grounds, bulbs, changed the fuses, traced what I think is the wiring,a green and brown wire and a green wire. and disconnected the tach from the truck wiring and the lights still do not flash. please send som ideas.