GMC 1976 ZEO 6083 Maintenance Manual page 430

6Y- 50
ENGINE ELECTRICAL
Figure 50-Secondary Wiring
Twist wire gently while observing ohmmeter . If the
resistance of the assembly is not within the specified
range, or if the ohmmeter reading fluctuates from
infinity to any value, replace the cable.
Timing Light Connections
When using a timing light, connect an adapter
between the No . 1 spark plug and the No . 1 spark
plug wire (figure 50). Connect the timing light to the
adapter. Do not pierce the plug bead . Once the insu-
lation of the spark plug cable has been broken, volt-
age, will jump to the nearest ground, and the spark
Figure 51-Distributor Cap Wiring
plug will not fire properly . The timing procedure
remains the same as the conventional breaker point
ignition system .
Compression Check
When making compression checks on engines
equipped with HEI, disconnect the ignition switch
connector at the battery terminal of the distributor
(figure 52).
Tachometer Connections
The tachometer terminal is next to the ignition
switch connector on the distributor cap (figure 52).
Most tachometers can be used, however, be sure the
equipment is compatible with the HEI system . The
tachometers without a relay cannot be used . If there
is any doubt as to whether you have the right ta-
chometer, a check can be made as follows :
a. Note reading on 1000 RPM scale.
b. Note reading on 5000 RPM scale.
c. Readings should be approximately the
same . If they are not, get another tachometer .
Connect the tachometer to the distributor cap
tachometer terminal and to ground . Some tachome-
ters must connect from the tachometer terminal to
the battery positive (+) terminal . Follow tachometer
manufacturer's instructions .
IGNITION
WIRE TERMINALS
TACHOMETER
WIRE TERMINALS
(DO NOT GROUND)
A-4004
Figure 52-Terminals on Distributor Cap