I have been having the old charging fault on my recently purchased 2002 Mondeo 1.8 LX

I have the ECU and Battery light on after a few seconds of firing it up....

I checked the Alternator firstly, and it charges OK with the plug on the back unplugged, so assume thats OK...

I checked the loom and that seems fine (from the alt into the main harness)

I have noticed that someone has bodged a wire into the ECU that looks like its designed to knock the ECU light out - so am guessing its been messed about with st some point!

My question is - can I replace the ECU with another from the same engine/year?

If so, do I need the key and transponder from the replacement ECU?

Help!