1. Automotive Electrical Systems
R. Bortignon

2. Electrical Circuits Contain 4 main parts… 1. Power source battery
alternator

3. Load 2. The load in a circuit is the part that does the work
load will always have some resistance
this resistance can be measured

4. Control 3. The control is what turns the load on or off…
opens & closes the circuit
may be installed on the ground side or the power side of circuit

5. Path
4. The path are the wires that connect the battery & alternator to the control and load devices in a circuit
frame/body of the vehicle is a path for the ground circuit

6. Circuit Protection
to protect the vehicle’s electrical system from excessive current flow, fuses are used
fuses open the circuit if current (amperage) levels exceed a predetermined level

7. Types of Fuses replace fuses with correct amperage rating!!!
cartridge fuses
blade type fuses
mini size
standard size
maxi size
mega fuse
ceramic disc fuses
see info on next slide
replace fuses with correct amperage rating!!!

8. Positive Temperature Coefficient Fuses
PTC fuse technology utilizes a polymer-based material to protect electrical circuits from excessive current.
During normal operation, numerous carbon paths within the polymer allow the device to conduct electricity.
As current through the PTC fuse reaches its rated threshold, the polymer material begins to heat causing the polymer to expand.
The resulting expansion breaks the carbon chains to reduce the current through the circuit to a small leakage current.
The increased resistance in this resettable fuse works to protect circuitry by limiting potentially damaging current.
When the fault (over-current) is removed from the circuit, the PTC fuse will reset itself thereby allowing current to flow through the circuit again.

9. many older vehicles use glass cartridge fuses

10. Fuse Panel Locations can be located…
under left side of instrument panel
in the engine compartment
many vehicles have fuse panels in
both locations

11. Fusible Links
special wire that breaks & opens a circuit when overloaded
insulation bubbles, melts & opens to expose wire
usually connected near the battery & feeds the fuse box(es)
must be replaced with correct rating
not all vehicles use fusible links
modern vehicles use maxi fuses instead of fusible links

12. Circuit Breakers
some circuits such as power windows & power seats use circuit breakers
circuit breakers reset themselves when current levels are back to normal
(do not need to be replaced like fuses)

13. Electrical System Service & Testing…

14. Testing Fuses 1) test with an ohmmeter set on the low scale
should have low/no resistance
be careful checking fuses visually

15. Testing Fuses 2) test with a test light
the key may have to be in the on position
the control/switch for the circuit may have to be on
test light should light up on both sides of the fuse
if only one side lights up – fuse is open
if neither side lights up – power is not reaching the fuse 3 1 2

16. Relays use a low current signal to activate a high current circuit
relay coil draws 150mA
contacts can conduct 30-50amps

18. Electrical Faults – High Resistance
circuit may not work at all
circuit may be dim or work poorly / slowly

19. Electrical Faults – Low Resistance
the load’s resistance is partially or totally bypassed
often referred to as a short
causes higher than normal current flow
usually causes fuse to open the circuit
frayed wire/bare insulation

20. Light Bulbs bulbs can be single or double filament
double filament = brake light & park light
note the offset indexing pins & 2 contacts
newer style bulbs do not require indexing

21. Testing Bulbs
often “blown” bulbs are easily seen during a visual inspection
sometimes a DVOM will verify the problem
use low resistance setting
polarity doesn’t matter
most bulbs will be ≈ 3Ω to 10Ω
you are looking for…
shorts (low/no Ω)
opens (high Ω)

22. Testing Headlamps older style sealed beams newer halogen, xenon bulbs
do not touch the quartz when replacing these!
1 connector is for ground – check for continuity to ground
2nd connector is for hi beam – check for voltage
3rd connector is low beam – check for voltage

23. Turn Signals
blinking function of the turn signals is controlled by turn signal flasher
may have 1 that controls turn signals & 4 way flasher
or 2 separate units
located in fuse box or under the left side of the dash
if one side flashes abnormally fast – check for faulty bulb on that side of the vehicle
if both sides flash incorrectly, the flasher unit may be faulty

24. Reading Wiring Diagrams
wire colors – jacket color followed by stripe color
connectors – identification numbers
usually + side of the circuit up top & ground at the bottom
ground number & locations

25. Using Component Location Function
component locator can be used to find connectors, relays, grounds, modules etc.
access electrical, then component location in Mitchell

26. Starter Circuit M B S terminal “B” (battery) is live at all times
terminal “S” (start) feeds power only when the key is in the starting position
“S” terminal will have a neutral safety switch in series for an automatic transmission equipped car
“S” terminal can also have a clutch safety switch in series for a manual transmission equipped car
“S” terminal may have remote starter switch or alarm disabling feature tied into it
terminal “M” (motor) has power during cranking only M B S

27. Starter Solenoid serves same purpose as a relay
is usually mounted directly on the starter motor
on Fords, it is mounted remotely on the inner fender

28. Voltage Drop Test
determines if too much voltage is being lost to poor connections
voltmeter is set to low voltage scale (0-2v)
meter leads are placed across a connection (circuit must be turned on during testing)
there should not be more than .1v loss per connection
both the positive and ground circuits can be tested this way

29. Hey Mr. B can I install…
the next 5 slides are helpful when adding electrical accessories to a vehicle

30. Adding Accessories
you and your students need to carefully consider what’s needed when adding amplifiers, driving lights etc.
add a relay to an existing circuit so you don’t overload the original circuit

32. Adding Fuses to Add-on Accessories
when adding additional equipment, add a relay to power the circuit
calculate the required fuse amperage
eg: 2 fog lights 4Ω each
amperage = 12 volts ÷ 4Ω = 3 amps through each light
3 amps X 2 lights = 6 amps total
6 amps flowing through circuit
multiply this by 1.5 to allow for any voltage surges
6 amps X 1.5 = install a 9 amp fuse

33. Hey Mr. B, do you have any wire?
determining wire gauge size for add-on circuits…
use a wire gauge table
always better to use a larger gauge size than is required 3' 5' 7'
10'
15'
20'
25'
up to 5 amps 18 6 16 7 8 10 11 14 12 15 20

34. Wiring Repair Tips
use grommets & loom to protect wires against abrasion
crimp & solder, then heat shrink
don’t rely on crimp only
on air bag systems & circuits to/from computer modules, follow manufacturer’s specific repair instructions

35. ISO 4 pin & 5 pin relay pin-outs …for your reference