Tic Toc Tac reads 1/2 RPM with MSD and filter
My apologies up front if this has been resolved somewhere, but I could not find this tach problem in a search or via google. MSD also has been of little help. I have a 1968 Camaro with a 383. I am using an engine works pro billet distributor with magnetic pickup, MSD 6AL-2 box (non programmable), tach adapter #8920, and an accel super coil. The tach is a repro OER tic toc tach from Classic industries. I purchased all the harnesses new and run console gauges. The tach worked fine with my Mallory dual point distributor. I am also running a single wire alternator. I also set the MSD box to 8 cyl. There is no arrow, so the dial is turned fully clockwise, which MSD says should be 8 cyl and the screwdriver slot is pointing to 8 cyl.
The problem I have now is that the tach works and stays smooth, but appears to be reading 1/2 the actual rpm. (400 @ idle, etc.). The tach responds smoothly on acceleration, but again appears to read 1/2 actual rpm. The tach does not work at all if I hook the tach lead from the MSD box to the tach signal wire directly. By the way, the tach lead from the MSD box is outputting 5V steady at idle, which MSD says is correct.
I wired the filter and box according to the MSD instructions for a voltage triggered tach, which I believe is correct. Any help would be appreciated.