Engine Hour Meter

TM 10-3930-644-14&P

Turning the switch to the "START" position,

These gauges provide quick response, direct

(which has a spring-loaded return causes

read-out dial indications of engine system

current to flow to the starter solenoid switch to

conditions during engine operation. If any of the

actuate the starter motor. As soon as the

units become inoperative, check the wiring

engine starts and the ignition key is released it

circuit, or determine whether the gauge or the

will automatically return to the "ON" position.

sending unit is defective by replacing with one

The engine will continue to run ii this position

which is known to be good.

until the ignition switch is turned to the "OFF"

position.

CAUTION

The current type ignition switch has a built in

Do not attempt to repair gauges or

interlock.

Whenever the switch is in "ON"

sending units, but always replace

position, it must be returned to "OFF" position

defective item whenever necessary.

before it can be turned to "START" position.

3. Engine Hour Meter:

The various ignition switch circuits can be

The engine hour meter is a direct reading type.

checked by removing wires from their respective

The unit records up to 9999.9 hours and then

terminals and holding test lamp probes to each

automatically returns to 0000.0. The four figures

terminal. If lamp fails to light, wire is defective

are read directly to record hours, while the figure

and should be repaired or replaced.

on the right records 10ths. of an hour.

WARNING

The engine hour meter starts recording when

This could be dangerous work.

the ignition switch is turned on. Meter will stop

Electrically it is always wisest to

recording when the ignition switch is turned off.

disconnect the battery when any

troubleshooting or maintenance is

If the hour meter does not operate or runs

performed on the electrical system.

erratically, check wiring for poor terminal

connections, a loose joining connection, bare or

5. Fuses:

frayed wires. Repair or replace as is required.

Fuse protection is wired into the horn and

Since the hour meter is a completely sealed unit,

instrument gauge circuits to prevent burning up

it will have to be replaced if tests indicate the

of this unit in case an electrical short circuit

meter is defective.

develops . The gauges are protected by a 10

ampere fuse and the horn and horn relay circuit

4. Ignition Switch:

is protected by a 10 ampere fuse. Both fuses

are located in clip retainers on a fuse block on

The ignition switch closes the electrical circuit

the right underside of the instrument panel. If

between the ignition coil primary winding and the

either the gauges or the horn fail to operate,

battery. Accordingly, it has one battery terminal

then the fusing should be checked first. If a fuse

lead, and one terminal lead to the ignition coil

is blown, it should be replaced with a fuse of

primary post and the instrument gauges.

identical rating.

Since the ignition switch operates the starter

6. Instrument Panel:

solenoid when turned to the extreme right, a

third terminal is used to run a lead to the starter

The instrument panel can be removed from truck

solenoid.

and reinstalled by following the typical procedure

as outlined below.

When the ignition switch is in the "OFF" position,

current is turned off between the ignition switch,

NOTE

the ignition coil and the instrument gauges. With

For safety purposes, the battery

the switch turned to the 'ON" position, current

should be disconnected to prevent

can flow between the battery, the ignition coil

the possibility of electrical shock.

and the gauges.

M-146-1

2-36