Vacuum switch B sends signals to the control unit when the vacuum falls below 30 mm. rt. Art.
Disconnect the #7 vacuum hose from the vacuum manifold and connect a vacuum pump to the hose.
Turn on the ignition.
Measure voltage between 8 (Yellow/Blue (+)) and 32 (black (-)) contacts.
If there is battery voltage, then see paragraph A), if not - item B).
A) Create a vacuum over 30 mm. rt. Art.
Measure voltage between 8 (Yellow/Blue (+)) and 32 (black (-)) contacts.
If voltage is present, replace vacuum switch B.
If there is no voltage, then vacuum switch B 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 yellow/blue (-) contacts on the main wiring harness.
If voltage is present, replace vacuum switch B.
If there is no voltage, then measure the voltage between Black/Yellow (+) and mass.
If there is battery voltage, repair the open in the Yellow/Red wire between the control box and terminal 2 of the control unit.
If there is no voltage, then repair the break in the Black/Yellow wire between the #1 fuse and the control box.