Hello from UK

If you are prepared to cannibalize your extender harness, cut wires off about 2-3" from connector and splice pin 1 to pin 2 and pin 3 to pin 5 (see image above)

Great, that is really helpful of you. I'll keep that as an option of I can't get a spare plug. If possible I'd prefer to keep the alarm together just in case... Or to maybe sell later to fund some more mods.
 
They are all the same on all triumphs from about 00 on
 
Geordies will lose to the mighty Arsenal today tho , and welcome to the forum Geordiebear !