I think Andy's got it.  From the 2001 GL1800 shop manual page 18-13 .  Look at the note at the bottom, emphasis added. 

INSPECTION

1. Remove the front fairing (page 2-10).

Check for continuity between the Green wire terminal

of the wire harness side bank angle sensor

3P green connector and ground.

There should be continuity.

• If there is no continuity, check for an open circuit

in the Green wire between the bank angle sensor

connector and ground terminal.

• If there is continuity, go to step 2.

2. Turn the ignition switch to “ON.”

Measure the voltage between the Red/white wire

terminal (+) of the wire harness side connector

and ground (–).

There should be battery voltage.

• If there is no voltage, check for an open circuit in

the Red/white wire.

• If there is battery voltage, go to step 3.

3. Measure the voltage between the White wire terminal

(+) of the wire harness side connector and

ground (–).

There should be battery voltage.

• If there is no voltage, check for an open circuit in

the White wire.

• If there is battery voltage, go to step 4.

4. Remove the two screws and the bank angle sensor

assembly from the right headlight.

5. Turn the ignition switch to “OFF.”

Connect the bank angle sensor connector.

Measure the voltage between the Red/white (+)

and Green (–) wire terminals.

• Place the bank angle sensor horizontal and turn

the ignition switch to “ON.”

There should be 0 – 1 V.

• Angle the sensor approximately 43 degrees to

the left or right with the ignition switch to “ON.”

There should be battery voltage.

• If you repeat this test, first turn the ignition

switch to “OFF,” then back to “ON” before you

try the test again.


Tony 

Never let a motorcycle take you somewhere your brain didn't go five seconds earlier.