Sven,
Don't know about ECUs on Morgans, but when jumpstarting a modern car take care because there are risks of ECU damage (apparently).
An RAC patrolman who came to my Subaru when the battery was flat, told me that the correct procedure having started your car is to leave the batteries connected and run both engines for five minutes or so to put some charge in the flat battery. Then switch off both engines and with your ignition off remove the leads. Then restart your car on it's own battery.
He said that they were taught that the ECU risk occurs when you remove the jump leads with the engine running because of the potential for sudden voltage changes and even spikes.
I'm not an expert but am passing on the advice that I was given even though it's not relevant to my toys which are all pre ECU!
Hope you get sorted out
Malcolm T
