I used the entire zetec loom, inlet and ecu, my car was mfi and i switched to the efi zetec management. There was a fair amount of wiring involved, had to put together a fusebox and mini-loom to feed the ecu, lambda and get the ignition lives and change fuel pump and ignition relays. On an efi 3i, I wouldn't say it's any easier really, we just use your existing fuel pump relay. Still needs the new fusebox and loom section.
It's not the only way to go about things but IMO, value for money-wise etc then using the management that previously had the engine running is the best way. Other people do it your way and use their old management and a conversion plate for the inlet altho I don't regard it as optimal compared to the "proper" setup that the engine was running on from the factory.
You'll then have to shell out for management that you can map to suit the new engines requirements, although again, there is an upside to that as when you inevitably decide you want more power, you can add your tuning goodies and have it mapped again to suit on a reasonable budget. and when you swap to a bigger lump, get just needs a re-map and you're laughing. Initial outlay is more, but if you're keeping the car then you're sorted for future modifications rather than having to keep swapping looms and ecu's.
I've got my engine in and running on the zetec setup, had it in for almost a year I think, I'll be running throttle bodies hopefully this year so I'll get it mapped, then once it's had a shakedown period with the 1.8 still in, I'll fit a 2.0/2.1 that I've been planning for a while and re-map it. Saves risking anything not working properly on the new engine and shagging it by fitting it all at once and something breaking.
