Chevrolet 10 1971 Series Chassis Service Manual page 440

ACCESSORIES 15-6
brown/white stripe wire from point C to D. It should
measure 40 ohms ± 2 ohms.
3. If a resistance either above or below the value indi­
cated is shown, the main wiring harness should be
replaced.
When disconnecting or reconnecting the
NOTE:
main wiring harness connector from the Regu­
lator, care should be exercised so as not to dam­
age the blade connectors or the wiring harness.
The disconnect may be facilitated by prying
carefully on the plastic connector with a small
screw driver.
4. Measuring the solenoid coil circuit resistance between
Point E (Hold Terminal) and ground, the ideal ohmic
resistance should be between 5 and 6 ohms. A reading
of less than 4 ohms indicates shorting in the coil
circuit. A reading of more than 7 ohms indicates
excessive resistance in the coil circuit. Either
extremity indicates replacement of the Regulator
assembly. The white main harness wiring from Point
F to G should also be checked for continuity.
S E R V O A N D V A C U U M SY S T E M C H E C K
To determine the condition of the diaphragm, remove
hose from the Servo Unit and apply 14 inches of vacuum
to the tube opening and hold in for one minute. The vacuum
shall not leak down more than 5 inches of vacuum in one
minute. If leakage is detected, replace Servo. To utilize
engine as a vacuum source, proceed as follows:
1. Disconnect Servo cable at carburetor and hose from
Servo, then connect engine vacuum directly to the
Servo fitting.
2. Note position of Servo diaphragm.
3. Start engine - - the diaphragm should pull in.
4. Clamp off engine vacuum supply line and check for
leakage.
The cruise release brake switch (vacuum) and connecting
hoses can likewise be checked using a vacuum pump.
10-30 CHEVROLET TRUCK SERVICE MANUAL