I am trying to wire in an MSD box to the MSD drop in EFI distributor. This is a little different though. I am not doing this in a thirdgen. I am simply using a 7730 computer to run the EFI system on this car. Well, the MSD box and old school style coil are already on the car and I intend to keep them and use them as is. My question is which wire does the MSD box need for RPM input? Should it be the EST wire(white I believe) or should it be the reference wire? I am hoping to only use the four pin connector on the ditributor not the two pin connector that would have gone to the coil. Thanks.

 

I would use the est wire so the computer would control the timing. But I have never done it.