Factory CJ7 tach with mpi

I read and read and all the "experts" said this couldn't be done. Well, I did it. Even the people (HESCO) who make the mpi kit for the 4.2 say it can't be done. Well, I did it and it works. Solid grey wire out of ecu to solid red wire on tach, red/white wire on tach to other cut end of solid grey wire going to coil. This works for obd 1 (1995 and older) 4.0L jeep motors