I added the stock type tach from Classic Ind. to my 69 and it burned up. Classic replaced it and it burned up too. I have a Pertronics Flame Thrower ignition which from what I have been told is NOT an HEI. HEI's have been known to burn up tachs installed without a filter. I have 12VDC from a switched connector on the fuse box, a signal wire to the - side of the coil and gnd. Any ideas???