Electrical Accessories Power accessories are designed many different ways Always use a wiring diagram to figure out how your system is designed Wiring diagram will allow you to decide how and where to test the system
Windshield Wipers Windshield wipers use an electric motor and linkages called the transmission. The transmission wiper linkages turn rotary motion to the back and forth of the wiper blades
Two speed windshield wipers Wiper motors use an off set brush for high speed Off set brush causes the armature to generate less Counter ElectroMotive Force (CEMF) Armature is the spinning part of the motor With less CEMF generated, the motor spins faster
OFF
Low Speed
High Speed
Low Speed
Two speed windshield wipers The windshield wiper switch directs current to the low speed brush, or the off set high speed brush Directing current to the offset brush will increase the windshield wiper motor speed
controlled by armature Park switch
Wiper Motor Park Switch The park switch will prevent wiper blades from stopping in the drivers vision when turned OFF The park switch is mechanically moved as indicated by the dotted line connecting the switch to the armature
controlled by armature Park switch
Wiper Motor Park Switch The wiper motor armature has a flat spot that allows park switch to ground only in the park position. Park position is with wiper blades at the lowest part of the windshield When windshield wiper switch is turned OFF the wiper motor will continue to run until the wipers are at the lowest spot on the windshield
Off Off
Low Speed
Low Speed
High Speed
High Speed
High Speed
Switch OFF Wipers UP (not park)
Switch OFF Wipers Down (Park Position)
Parking Wiper Blades Wiper motor can reverse directions Slots in the transmission linkage will pull blades down lower than normal travel when the wiper motor is reversed This is done to hide wiper blades from driver view when in Park position
Off Position
On - Low speed - Top brush is ground
On - Low speed - Park switch cycles
On - Low speed - Park switch cycles
On - Low speed - Park switch cycles
` OFF Top Brush Positive Motor reverses direction Wipers will Park in lower than normal position
Gauges Explore the operation of a bimetallic dash gauge As more current flows through bi metallic gauge it heats up and bends to show high pressure (oil pressure gauge) high temperature (engine temperature gauge) full gas tank (fuel gauge)
COLD High resistance
HOT Low resistance
Gas Tank Sending Unit Empty High Resistance
Gas Tank Sending Unit Full Low Resistance
Bimetallic Gauges As voltage increases what happens to amp flow? Many dash gauges use an Instrument Voltage Regulator (IVR) to keep a constant 5 volts to the gauges
Diagnose dash gauges Notice if all gauges are out or only one Use a test light to ground the sending unit wire Test lamp will flash as instrument volt regulator operates Do not use this technique with digital dash
If only one gauge is bad, suspect sending unit or wires to the sending unit
If all gauges are bad, suspect problem common to all gauges (fuse, IVR if used, ground, printed circuit of dash panel)
If only one gauge is bad, suspect sending unit or wires to the sending unit
If all gauges are bad, suspect problem common to all gauges (fuse, IVR if used, ground, printed circuit of dash panel)
Gauges with 2 wires will be bi metallic sing an instrument voltage regulator. These show high with more current and low with less current. Gauges with 3 wires will be magnetic. 3 wire magnetic gauges can show high OR low as current increases
If all gauges are bad, suspect problem common to all gauges (fuse, IVR if used, ground, printed circuit of dash panel) 3 wire gauges use two or more coils to form opposing magnetic fields that will move the gauge needle. Instrument voltage regulator is not needed as changes in system voltage will affect both magnetic coils equally
If all gauges are bad, suspect problem common to all gauges (fuse, IVR if used, ground, printed circuit of dash panel) Two Coil Magnetic Gauges
High resistance in sending unit
Low resistance in sending unit
Three Coil Magnetic Gauges Sending unit works Opposite from other gauges
High resistance in sending unit
Low resistance in sending unit
Diagnosing Gauges Sending unit is most common cause for one gauge to become inoperative To confirm a bad sending unit locate the unit
Diagnosing Gauges Gauge should go full travel high or low (depends on style of gauge) Ground sending unit wire with test lamp Gauge should go to other side of travel If gauge changes it proves gauge and wires are good and replacing sending unit will fix gauge
Diagnosing Digital Gauges Electronic controls can be damaged by grounding sending unit wire Use diagnostic charts and scan tool to diagnose digital gauges Scan tool can often confirm operation of digital gauges (functional test)
Instrument Clusters Use caution when handling printed circuit boards Finger prints can cause high resistance and eventual open circuits in printed circuits
Speedometers Changing tire size will change calibration (cause speedometer to become inaccurate) Different size drive gears are available to correct for tire size and differential ratio Digital speedometer can be re flashed to accept larger or smaller tire diameter Tires other than stock sizes can cause problems with transmission and brake controllers
Optional Type Accessories Heated Windshields Uses alternator at high voltage While windshield heats all alternator output is directed to windshield Runs close to 100 volts
Heated Back Glass Operates at normal charging system voltage Most common problem is open circuit in heater grid
Power Windows/Seats Use of wiring diagram is critical to diagnosis Slow turning motors will cause increased amp draw Check for binding mechanisms Self re setting circuit breaker protected
Warning Systems Most systems will ground a buzzer or warning lamp