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Sec. 7
Page 114
GM COACH MAINTENANCE MANUAL
WIRING AND MISC. ELEC.
TP-7132
Figure 13-Electric Speedometer Drive
Unit
Electrical currents from drive unit energize
two pairs of coils in motor unit causing magnetic
rotor to rotate at exactly same speed as mechan-
ically driven unit.
Since motor is coupled to
speedometer head, rotation is transformed to a
reading on face of calibrated speedometer head.
Thus, a synchronized electrical drive supplants
the standard drive cable.
TESTING
For testing speedometer electrical units (us-
ing battery of 12 volts}, plus or minus one volt
variation is permissible.
The maximum current
consumption should not exceed two amperes.
Jam nut, located . at point four wire conduit
fastens to connector plugs; should always be kept
tight.
The connector plug body grips cable insu-
lation and prevents conduit coming loose from
connector plugs due to rough handling which would
cause loose connections.
A test light (1568147) should be used to test
electric speedometer.
If
speedometer ceases to
function proceed as follows:
1. Check test light bulbs with battery to be
sure they are not burned out. Check 6 amp. fuse
in feed wire to drive unit to be sure it is not
burned out.
2. Pull four-contact plug out of top of drive
unit and insert plug on end of light cable
in
its
place.
3. Turn control switch to
"RUN"
position to
energize drive unit.
4. Disconnect flexible drive shaft at trans-
mission. Trun drive shaft slowly by hand.
If
lights
alternately grow bright and dim, the drive unit is
functioning properly.
TP 2828
Figure 14-Electric Speedometer Motor Unit
5. Remove test light cable plug from drive
unit and reconnect cable to drive unit.
6. Disconnect cable plug from speedometer
head motor and connect to test light cable, using
double end male adapter chained to end of cable.
7. Again turn drive shaft slowly by hand. If
lights alternately go bright and dim, wiring be-
tween drive unit and head is good and trouble
should be in head unit.
8. Always be sure that plugs make good con-
tact when connected.
9.
If
lights fail to check when connected to
unit, check feed and ground connections at drive
unit for tightness; also for broken flexible drive
shaft.
10.
If
lights check when connected to
drive
unit but not when connected at front of cable, care-
ful check should be made of electrical cable for
broken wire or loosen connections where wires
attach to sockets.
With
above procedure, it will be easy to de-
termine whether trouble lies in drive unit, in con-
nector plug and wiring, between drive unit and
motor unit, or in motor unit and speedometer head
assembly.
NOTE: If
speedometer test fixture with
master head is available, the speedometer
can be tested with master speedometer
reading 60 miles per hour.
If
speedometer
calibration is not satisfactory when speed-
ometer is driven mechanically, head may
be recalibrated by an authorized United
Motors Service Station. Speedometer cali-
bration discrepancies have no connection
with the electric drive unit, providing the
speedometer head and motor unit are not
binding, which is easily discovered by ex-
cessive pointer fluctuations.
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