The messages from The Judge are sent to your Computer on Pin 2.

The messages from your Computer to The Judge are sent on Pin 3.

When the Judge is first powered up, the Judge runs through its distinctive
light show: the rotation through the red lane lights, plus some simultaneous
hits on all red lights. Meanwhile it sends a welcoming message which contains
the Firmware Version number. It also invites you to test the two way communication
by sending the asterisk symbol.

               *

Any time The Judge receives an asterisk, it causes an unconditional
reset, which inititates the distinctive light show. The light show also
is initiated upon first powering up, and of course at the end of every
display of race results.

By shorting Pins 2 and 3 together up at the computer end of the cabling,
you are sending The Judge's welcome message back to itself. When
it gets to the part about sending the asterisk, Whoa! It immediately
breaks off from what it was doing, and goes through another reset
light show.

So, with the paper clip in place, you get a double light show. This
proves the cable (both directions) is fine, and also shows the Judge
microprocessor is alive and well.

It does not verify a possible cable problem with the magnetic switch,
but there are other tests for that.