Cessna 170 Service Manual
Electrical System
TROUBLE SHOOTING THE BATTERY SYSTEM.
BATTERY DOES NOT SUPPLY POWER TO BUS WHEN MASTER SWITCH IS ON.
Dead battery: Check specific gravity of electrolyte. Gravity reading should be at least 1.256, which indicates
a 75% charge at normal temperature. Replace or charge battery. Check charging rate of generator.
Defective master switch, battery solenoid or wiring: (IF you are CERTAIN the battery is good and well
charged) Short the battery solenoid terminal that is wired to the master switch to ground. This is the small
terminal of the solenoid. If the solenoid does not operate, check the jumper wire connecting the solenoid
coil to the "hot" solenoid terminal (two small terminal models only). If the solenoid does not activate, repair
defective wiring or replace solenoid. If the previous test activated the solenoid then check master switch for
continuity across circuit terminals. (Caution: Note the correct wiring schematic for the cockpit master switch,
re: two circuits. See above MASTER SWITCH commentary notes.) Check for good ground continuity
between Master switch grounded circuit and battery ground terminal.
Faulty battery cable: Inspect the battery cables for good connection. Clean and/or Replace cable,
reconnect.
Battery Box: Check battery box drain line to be open and clear of insect nests, or rubbish. Clean battery
box with battery removed using water and baking-soda solution. Rinse battery box thoroughly with clear
water. Inspect interior of box for condition of acid-resistant paint (if equipped.) Renew as necessary.
Reinstall battery.
BATTERY SUPPLIES POWER TO BUS BUT WILL NOT CRANK ENGINE
Low Battery. Check specific gravity. Charge battery
Faulty battery cables, Inspect for corrosion and poor connection. Repair wiring. Clean and reconnect
Battery cell shorting under load. (This cause is very difficult to detect. Even a good battery connected to
a shorted battery will behave similarly. Only when a shorted battery is completely removed from the system
will operations return to normal.) Test battery with a load tester. Replace defective battery.
Defective starter contactor or solenoid. On aircraft with starter switch check operation of switch and
solenoid. Replace switch. Replace solenoid.
BATTERY USES EXCESSIVE AMOUNT OF WATER. Charging rate too high. Test voltage regulator or try
a new unit. Adjust or replace regulator,
NOTE: Voltage regulators are adjustable, however adjustment should not be attempted unless proper
equipment is available. Refer to Delco-Remy service bulletins and see Voltage Regulator section for
instructions.
REMOVAL AND REPLACEMENT OF BATTERY
a. Remove the battery box cover and open cover. b. Disconnect the ground cable from the negative
battery terminal.
Always remove the ground cable first and replace it last to prevent accidental short circuits.
c. Disconnect the cable from the positive terminal of the battery.
d. Lift the battery out of the battery box.
e. To replace the battery, reverse this procedure.
CAUTION: Storage batteries are filled with corrosive electrolyte, usually sulphuric acid. Wear protective
goggles and clothing. Avoid contact with electrolyte. Prior to working on batteries, provide a ready source
of clear water to flood accidental spills. Electrolyte may be neutralized with a solution of baking soda and
water. Do NOT contaminate the battery’s electrolyte with baking soda solution or it will be damaged.
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