[eapcpa]

I am using twin MSD on my twin plug ignition. I am also using the MSD tach adapter model 8920 because the JB racing distributor has magnetic pickups. Tach works great, in fact I have an on/on switch so I can switch the tach signal back and forth to monitor output from each MSD box. My theory is that if a box fails, the tach signal will fail and I won't be stuck running on six plugs. The problem is that I cannot get the deceleration microswitch working so I get a steady snapping and popping noise when I let off the throttle. It does sound good to some but it gets pretty annoying. I have picked up the black and purple wire going from the 14 pin plug on the rear relay panel directly to the tach. I tried picking up the black and purple wire from the other 14 pin connector from the engine harness as that runs through the speed sensor and and microswitch and then then up to the tach. That causes the tach to not work. Unfortunately I did not check to see if that allowed the microswitch to work. I thought I would ask for someone more knowledgeable to advise me. Do I need to split the signal from the MSD tach adapter to the speed sensor and the tach or will this cause a problem. I do not want to let the smoke out of any of these little electronic devices as that usually causes them to stop working and once released you can't put the smoke back into them, so I am told. I already let the smoke out of the first MSD tach adapter but that was another story. It only cost another $60 to replace. Any help is appreciated.