Field Relay Checks And Adjustment; Closing Voltage Adjustment; Field Circuit Resistance Wire Checks - Chevrolet 10 1971 Series Chassis Service Manual

ENGINE-ELECTRICAL 6Y-12
a. Test lamp glows - problem is in regulator. An
open circuit in regulator or relay is stuck closed.
Replace regulator.
b. Fails to glow - problem is in wire between " F "
terminals on generator and regulator or in field
windings. Go to Step 3.
3. Disconnect test lamp at connector " F " terminal and
connect to " F " terminal on Delcotron (fig. 7c, Step
3), and note lamp:
a. Lamp glows - an open circuit in wire between
" F " terminals - correct as needed.
b. Fails to glow - Delcotron field has open circuit
see "Service Operations" to repair.
This test lamp procedure may be used on
NOTE:
lamp type circuits and on ammeter circuis.
If Lamp Fails to Go Out, or if Ammeter Shows Dis­
charge the Possible Causes are:
1. Loose drive belt - adjust as necessary.
2. Faulty field relay - (see relay test and adjustment).
3. Defective Delcotron - (see Delcotron output test).
4. At normal idle - parallel resistance wire open (see
Resistance Test). Ammeter models the initial field
excitation wire to "ACC" terminal is open.
5. Switch off - positive diode shorted (See Diode Test).

Field Circuit Resistance Wire Checks

The resistance wire is an integral part of the ignition
harness. However, the resistance wire is not solderable;
W IRIN G H ARNESS
C O N N ECTO R
Fig. 8c-Testing Field Relay
it must be spliced with a crimp-type connector. It is
rated at 10 ohms, 6.25 watts minimum.
The check for an open resistor or field excitation wire
(connected to the ignition switch "A " terminal) is as
follows:
1. Connect a test lamp from the wiring harness con­
nector terminal "4 " to ground as shown in Figure
9c (Step 1).
2. Turn the ignition switch to the "ACC" position and
note test bulb.
a. Test lamp glows - resistance is O.K.
b. Test lamp does not glow - the resistor is open
circuited - note also that dash lamp does not glow
during this test because series resistance of the 2
bulbs causes amperage to be too low.

Field Relay Checks and Adjustment

To check for a faulty relay proceed as follows:
1. Connect a voltmeter into the system at the regulator
No. 2 terminal to ground (fig 8c).
2. Operate the engine at fast idle (1500 to 2000 rpm) and
observe voltmeter reading.
3. If voltmeter shows zero voltage at regulator, check
circuit between No. 2 terminal on regulator to " R "
terminal on Delcotron.
4. If voltage at regulator exceeds closing voltage speci­
fication and light remains on, regulator field relay is
faulty (Refer to specifications). Check and adjust
regulator as follows:

Closing Voltage Adjustment

1. Make connections as shown in Figure 9c using a 50
ohm variable resistor.
W IR IN G HARNESS
CO N N E C T O R
Fig. 9 c -F ie ld Relay Closing Voltage Tes.
10-30 CHEVROLET TRUCK SERVICE MANUAL