As HAX showed in his doc, you just unplug it and the seat removal sensor just clips out. You ideally need that shorting plug to remake the system wiring though, not sure what you do without that? The dealer on fitting is supposed to send it to the alarm manufacturer but they gave me mine.
Indeed from reading the instructions, it would appear that one definitely needs that for removing said alarm, else the electrics are not connected back up. Hmm Looks like maybe one can't easily remove the alarm (which I did wonder about else it would be just too easy for thieves to disable).
Wonder if one can purchase a new shorting plug though. There seem to be two possible plugs listed T2500396 and T2500050, but which is the right one (or even the one for a Gen-1) I don't know, it may even be another part number. Think I'll have to get my mate to ring a dealer's to find out, as no doubt they will need to verify ownership before they'll sell such a part.
@XCaTel - does your shorting plug have a part number on it by any chance?
