You guessed right.
The problem is that the little yellow plug doesn't appear on any schematics I have ever laid my hands on for a MA61.
I have a strong suspicion that the little yellow socket that it is supposed to plug into was also grafted onto the chassis loom. Hence it looked like a plug in/out job but wasn't.
I guess the only way is to rip out the glovebox & hunt around for the 'little yellow socket' (although I thought I did that a few months ago & couldn't find anything that remotely resembled it).
Thanks for the tip though.