the coil interface goes between the stock ignition module and the coil pack. it is used to make wiring the msd DIS4 ignition into your car easily. makes less cutting into the stock wiring harness. the DIS4 system has a few nice features. one is it has a built in 2 step for starting line rpm. you hold a button and brake, then hold the throtle to the floor. it will only go to the rpm that you set it at. then just let go of the button and brake and it goes to WOT. this works great for drag racing and best if you have a line lock and have both the line lock and the 2 step wired to the same button. this makes for consisent and awesome launces.
second is it has a built in timing retard, you can set it to retard the timing at a certain rpm and set number of degrees to help with high boost and to prevent detonation.

i bracket race and i am very seriously thinking about getting this set up for my bonny.