Automotive Electrical Systems R. Bortignon

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

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

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

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

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

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!!!

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.

many older vehicles use glass cartridge fuses

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

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

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)

Electrical System Service & Testing…

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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