Whats this for?

Found a connector near the ECU and just windered what its for if anyone knows?

Diagnostic connector for the 993cc -

Short out the two brown wires, then the engine warning light will flash fault codes at you.

Ah! Thanks, never crossed my mind about that. Apart from shorting the wires out is that where one of the code reading machines would just plug in?
Reason I was looking down there was not for that but trying to find a wire to connect to the horn for my alarm. Can see where it is at the front but then it dissapears inside somewhere. Any ideas best place to join into it?
Also it needs to connect to the door light switch, I know where those cables are but I have two choices, positive or negative switched? Any Ideas which the hijet is or how I can test it to find out. Electrics are not my strongest point...but willing to have a go!

TIme to play with a multimeter

Was going to today but rain stopped play!