Vacuum switch A sends signals to the control unit when the vacuum falls below 80 mm. rt. Art.
Disconnect the #2 vacuum hose from the vacuum manifold and connect a vacuum pump to the hose.
Turn on the ignition.
Measure the voltage between 1 (Green/Yellow (+)) and 32 (black (-)) contacts.
If there is battery voltage, then see paragraph A), if not - item B).
A) Create a vacuum over 80 mm. rt. Art.
Measure the voltage between 1 (Green/Yellow (+)) and 32 (black (-)) contacts.
If voltage is present, replace vacuum switch A.
If there is no voltage, then vacuum switch A is OK.
B) Switch off the ignition.
Disconnect the 4-pin connector on the control box.
Turn on the ignition.
Measure the voltage between Black/Yellow (+) and Green/Yellow (-) contacts on the main wiring harness.
If voltage is present, replace vacuum switch A.
If there is no voltage, then measure the voltage between Black/Yellow (+) contact and weight.
If battery voltage is present, repair an open in the Green/Yellow wire between the control box and terminal 1 of the control unit.
If there is no voltage, then you should repair the breakage of the Black / Yellow wire between fuse No. 1 (15 A) and control box.