I bought my 93gs300 in chicago and believe me, it is a handyman's special. the tach has never worked and I just bought a Sun tach. I do not know which terminal is the "negative" on either the coil or the other silver-colored device that is part of the firing assembly. Can anyone help me as to which wire on my car will send the signal to this new tach??? As always, you guys are a great source for help! Marcus