Did my best to comb through this thread before posting, so I apologize in advance if this scenario has already been addressed.
Recently got my wasted spark setup installed after chasing a weird stumbling behavior (which wasted spark seems to have made better but didn't fix, but that's a story for a different thread).
The car is a 1993 volvo 940 turbo. I've followed the wiring diagram posted by byneset for using the bosch 2x2 coil and the j702t ignitor, the car runs but I have a question about two of my connections. For the tach and switched 12v connections for the j702t, I used the red/white stripe and blue colored wires from the stock coil. With the coil removed, the car starts and runs with these connections but the tach doesn't read. With the stock coil in place and these connections the car runs and the tach reads, but unfortunately this also powers the stock coil and things get a little sparky. Do I need to wire a dummy relay in place of the coil to use these connections and have a working tach? Or should I find different switched 12v and tach signal connections and leave the stock coil wires disconnected? Thanks