Chevrolet 30 Series 1967 Service Manual page 360

ENGINE-ELECTRICAL 6Y-T2
Fig. 9c— Delcotron Diode and Field Test
or open field or shorted diode but will not in­
dicate a failed open diode. If output was low
and following tests show good, refer to service
operations to determine cause and repair.
1. Disconnect battery ground cable at battery.
2. Positive diodes (Test A) connect an ohmmeter be­
tween " R" terminal and " BAT" terminal and note
reading, then reverse the leads at same terminals
and note this reading. Meter should read high re ­
sistance in one direction and low in the other.
3. Negative diodes (Test B) connect ohmmeter between
" R" terminal and " GRD" and note reading, then
reverse the leads and note this reading.
4. Open Field Check:
5. If above tests indicate a defective Delcotron, remove
INDICATOR LAMP/INITIAL FIELD
EXCITATION CIRCUIT TESTS
5.5"-6.2" Systems
On standard models the indicator lamp circuit provides
initial field excitation (causing lamp to glow). The light
is cancelled by closing the field relay which applies
battery voltage to both sides of bulb (bulb goes out).
The indicator light should glow when ignition switch
is "ON" and go out almost immediately when engine
starts.
Ammeter equipped vehicles use the same initial field
excitation and control circuits as the indicator lamp
except the lamp is omitted. The continuity tests on both
type vehicles can be made as follows:
If Lamp Fails to Glow or Ammeter Fails to Function
the Possible Causes are:
1. Faulty bulb or bulb socket.
2. Faulty ammeter.
3. An open circuit in wiring, regulator, or field.
4. A shorted positive diode - (may also cause glow
Meter
Fig . 10c—In itia l Field Excitatio n C irc u it Tests
should read high in one direction and low in the
other.
NOTE: A high or low reading in both directions
indicates a defective diode.
a. Connect an ohmmeter from " F " terminal to
" GRD" terminal stud and note reading on the
lowest range scale. Meter should read 7 to 20
ohms.
b. If meter reads zero or excessively high re s is­
tance the Delcotron is faulty.
and completely check Delcotron as outlined under
" Service Operations."
CHEVROLET TRUCK SERVICE M ANUAL