Took the car to the track. Had to bypass 685 box (again) because it smoked. No problem, if it breaks up I will shift early or park it. Realize I have no tach now. So I remove connector from box and hook to negative side of coil. Start car and we are good or go. Halfway to track tach needle is jumping around. CAR IS NOT MISFIRING. Farther I go, worse it gets. This is an Autometer Pro Comp 5" tach with shiftlight. I get to thinking... hmm. MAYBE this tach is what is smoking my 685 boxes! Is that probable? Get to track and ready to run. Start car and tach reads 400rpm steady! Car is idling at 1100. Make pass and shift by ear. (yes, I am that old). God only knows what I shifted at, but rods are still in it so must have guessed right. LOL. You guys ever have a tach cause ignition woes? I had another fella tell me his tach shorted and blew his exhaust off on a nitrous pass!