Cessna 170, Service Manual

Cessna 170 Service Manual 
Electrical System 
 

11

e.  Re-install the lamps within their channels and install the adjustment screws by counting the same 

number of turns as was required during removal.  (See Appdx EL, Fig. EL-04 for preliminary 
adjustments.) 

 
NAVIGATION LIGHTS

. The navigation lights are located on each wing tip and on the trailing edge of the 

rudder.  Some early aircraft are equipped with a flasher, which blinks the lights at a regular rate. A single 
switch controls the navigation lights.   If flasher-equipped, they are controlled by a single three position pull 
type switch.  
 

NAVIGATION LIGHTS FLASHER

. The navigation lights flasher is mounted behind the panel on the glove 

box. Early aircraft are equipped with a Narco thermal operating type flasher. The Narco flasher requires a 
noise filter when used in aircraft with radio equipment. The Narco flasher is no longer available and when 
replacement is required a transistor type should be installed. Some aircraft are equipped with a Van Duesen 
flasher, which has a replaceable thermal type timing cartridge. The cartridge actuates a relay, which controls 
the lights. If the timing cartridge fails the lights remain on, providing fail-safe operation.  
The latest flasher is a transistor type, which does not use mechanical switching. The conducting properties 
of the transistors are used to turn the navigation lights on and off. Two transistor circuits are used to provide 
two-circuit navigation light switching. Each of the circuits triggers the other into operation. This flasher also 
provides fail-safe operation.  Navigation light flasher systems have been largely superceded by more 
modern anti-collision light systems. 

 
ROTATING BEACON

.  Rotating beacons (anti-collision lighting) was not required but was an option during 

certification of the 170, but most owners have subsequently retrofitted these aircraft with such systems.  The 
rotating beacon is mounted to the fuselage, either/or top or bottom.  Most units are either Grimes or Whelen 
and mount similarly with three machine screws through the case into a mounting ring.  The lens may be 
removed by loosening the clamp and the bulb(s) may then be accessed for replacement.  The usual difficulty 
with Grimes-type units is failure of the drive motor that rotates the bulbs point of focus thereby creating the 
flashing effect.  When these motors fail it is usually more economical to simply replace the entire unit with a 
later model.  Most owners find the Whelen direct-replacement strobe system the best solution.   

 
INSTRUMENT LIGHTS, MAP LIGHT AND DOME LIGHT.  

Several types of instrument light have been 

utilized in Cessna 170 aircraft.  .  Early instrument panels incorporated individual indirect lighting within the 
floating instrument panel.  Some later models were equipped with dual, ultra-violet, fluorescent lamps, 
however most models utilized plain incandescent lamps within an overhead console either mounted within 
dedicated sockets and directed through a red lens at the instrument panel, or mounted within Grimes 
“torpedo” lamp assemblies and directed at the panel.  This latter system is the most common.  Instrument 
lighting is controlled through a rheostat mounted on the lower instrument panel.  This rheostat is a 
resistance-wire-wound ceramic variable resistor.  By increasing/decreasing the resistance experienced by 
the supply current, the rheostat varies the brilliance of the lighting.   
  The Map light is a “torpedo” Grimes lamp assembly mounted on the left doorpost and operated by a slide 
switch.  The assembly may be focused by adjusting the small knob on its upper end, and the entire unit may 
be directed about the cockpit by moving it on it’s mounting pedestal.  The friction of the pedestal is adjusted 
by a small clamp-and-screw with a small screwdriver.   
The lamps in both the Grimes Map light and the Grimes overhead Instrument lights may be replaced by 
simply pulling the “torpedo-tube” from it’s base/pedestal.  Only GE-67 bulbs should be used for replacement.  
These bulbs are rated at 3 candlepower. 

 
COMPASS LIGHT

.  The compass is internally lit and it’s light is controlled by the same rheostat as the main 

instrument lighting.  It consists of a T 1-1/4 size GE-330 bulb.  This lamp may be replaced by removing the 
false instrument panel, rotating the flat lamp-cover away from its closed position, and removing the lamp.  
Reversing the procedure completes the installation. 
 

REMOVAL AND REPLACEMENT OF NAVIGATION LIGHTS.  

Remove the navigation light cover being 

careful not to allow the colored lens to fall and break.   Using a protective cloth, grasp the navigation lamp 
and push it in, rotating it 1/3 counterclockwise and pulling it from it’s socket.  Examine the socket for 
corrosion and dirt, removing any found with a pencil eraser.  Lubricate the socket bottom VERY LIGHTLY 
with Dow Corning DC-4 on a cotton swab.  Do NOT overdo this.  Install the new lamp being careful NOT to 
touch the glass with your fingers, as any contamination will shorten the life of the lamp.  If oil, or 
contamination should get on the lamp, remove it with alcohol.  Clean the interior of the colored lens with 
glass cleaner and reinstall with its retainer/cover.  

Note

:  Early aircraft utilized the No. 1512 lamp in the 

navigation light position.  This is a 12/14-volt, 21-watt lamp and was the original lamp specification for the