964 wiring diagram and from battery question

[parkertseng]

Hi

I am trying to take a measurement of voltage difference across the car.
To find the reason of voltage at battery is lower than alternator specially at initial start up for about 14.1v at alternator and 13.5v at battery post.
It took about 5 to 10 minutes of drive till the battery voltage raised up to 13.9-140v.

Looking at the wiring diagram where can I find this squared box without number in it, a solder or bolt joint.

Thanks