If you are using the original engine's ECU you must ensure you get the corresponding immobiliser unit form the same car (along with the immobiliser key fob). They are a matched set and you cannot cross them with other sources. Here you can see a picture of the Lucas 5AS unit which sits inside the car underneath the dash.
	Since we are going the tuning route, we replaced the standard Rover MEMS ECU with a programmable one from Emerald Cams. This little ECU really is the dogs bollocks; a fully mappable fuel & ignition ECU with soft/hard cut rev limiters, shift light, tell tales and a great piece of programming software supplied all-in. It's completely Rover MEMS pin compatible so it's just a case of plug it in and go.
You'll also be wanting one of these - a MEMS relay module. This is basically a collection of 3 relays - one for the ECU, one for the fuel pump and one for the ignition. The immobiliser and ECU are responsible for enabling these relays when you de-immobilise the car, so they're pretty important.
	The copper chaos that IS the auxilliary fusebox (found under the steering column). All the plugs on here are unique so it's hard to plug the loom into the wrong part of the fusebox. The purpose of each fuse can be found in our trusty Haynes manual (don't leave the garage without it). The yellow plastic bracket holds in the SRS airbag fuse and is intended to stop Repmobile Rover Man from tinkering with it. Needless to say, we won't be needing it.
This is the main fusebox, located in the engine bay. This is where your main feed from the battery comes in (thick brown wire on right). From here the power is fed off to things like the ignition barrel and MEMS relay module. Check all the fuses are okay in it. You won't need a full set as some fuses will be redundant when in Robin Hood guise. Your Haynes manual explains the purpose of each fuse.
	If you're not using the standard Rover steering column & ignition key, you'll be stuck when you come to find out where to wire the ignition barrel (as this isn't detailed in the Haynes manual OR the Rover schematics). Well, the ignition barrel is wired up in two places - one of these is to the auxiliary fusebox itself, as indicated in this diagram.
The second place to wire your ignition barrel is into the main loom, half way along the stretch of cabling that runs across the dashboard. Look for the two brown/purple wires accompanied by a single white/red. The picture shows the original connector that was on the end of them. The brown/purple wires are constant lives from the main fusebox so be careful once you've got the battery wired up. The white/red is the cranking signal for the starter motor. Apply a +ve current and the starter will turn.