[b3lha]

The Plug that you have labelled 1 is "Check Connector (Manufacturing) B34".

Presumably they use this to test the control units before the car leaves the factory. It duplicates the wires in the yellow select monitor connector B35 and the black diagnostic connector B36 (#2 in your picture). There are also some other wires running from it to the ABS, Cruise, TCU, Steering and Airbag units. I've never seen the pinout of B34 documented, so I went through the wiring diagram and I've listed them below.

B34 Manufacturing check connector pinout
1 ABS
2 ABS
3 ABS
4 ABS
5 Cruise = B35-4
6 TCU
7 Steering = B36-7
8 ??? not connected on my car
9 Airbag
10 ABS/TCU
11 ABS
12 ABS
13 Receive Data (ECU/TCU/Cruise/AirCon) = B35-3
14 Transmit Data (ECU/TCU/Cruise/AirCon) = B35-2
15 ??? Possibly +12v
16 Ground
17 ECU = B36-1
18 Steering = B36-5
19 ??? not connected on my car
20 Airbag = B36-3

B35 select monitor connector pinout
1 ??? not connected on my car
2 Transmit Data (ECU/TCU/Cruise/AirCon) = B34-14
3 Receive Data (ECU/TCU/Cruise/AirCon) = B34-13
4 Cruise = B34-5
5 +12v
6 ??? not connected on my car
7 ??? not connected on my car
8 ECU
9 Ground

B36 diagnostic connector pinout
1 ECU = B34-17
2 ECU
3 Airbag = B34-20
4 4WS
5 Steering = B34-18
6 Steering
7 Steering = B34-7
8 Seatbelt
9 Airbag
10 Ground