I have a 1999 7.4 MPI.
I am planning to remove the MPI and go with a Carb.
Can I simply unplug the MPI injector harness, the ECU, and the other sensors related to the MPI?
or
Do I need to purchase a new engine harness?
Thanks,

I know some of you guys have done this...

The Ecu controls the ignition, You will need either a new harness and merc Thunderbolt ignition module or msd type box or something in its place.

You will also need a new fuel pump

http://www.fullthrottlemarine.com/

They did my 98 502. Call or send him an email. Ask for Bob Loyd.

Thanks guys,
I know that I will need a different fuel pump.
I think that I can use the existing distributor with it's built in Delco "backup" ignition module.
Really just hoping that I don't need to hack up or replace the engine wiring harness.

Basically the EFI part of the harness makes the conections to the Distributor, coil, knock sensor, fuel pump relays, water temp sender for gueage, oil preasure sender for guage and the gear lube bottle sensor. ( and to the throt pos sensor, MAP, engine coolant temp and IAC but you won't be using these anymore on a carb engine)

If you remove the efi harness you will need to make something up to these connections to the engine part of the harness. You will need something to control the ignition, MSD can be hooked into the ecu conector I think, ask them.

efi harness diagram

http://www.mercruiserparts.com/Show_...NESS+%28EFI%29

engine harness diagram

http://www.mercruiserparts.com/Show_...S+%28ENGINE%29

Thanks for the info,i'm considering doing something similar thia winter,I don't want to reuse or hack up the original efi harness,i want to save it for when i re-install my stock efi motor for resale,smitty