The electrical system covers the sensors, switches, ignition parts and components the engine computer uses to run the car. Here you will find aftermarket sensors, coils, plugs, ignition leads, ignition switches, starters and electrically controlled valves for American cars.
In this guide: A/C pressure switches, ABS sensors, Air bag clocksprings, Blower motor resistors, Camshaft position sensors, Camshaft synchronisers, Coolant temperature sensors, Crankshaft position sensors, Cylinder head temperature sensors, Fan control modules and relays, Fuel injectors, Fuel pressure regulators, Fuel pressure sensors, Fuel pump driver modules, Fuel pumps, Glow plugs, Idle air control valves (IAC), Ignition coils and distributors, Ignition lock cylinders and switches, Intake air temperature sensors, Knock sensors, Light switches, Manifold runner control valves, MAP sensors, Mass airflow sensors (MAF), Neutral safety switches, Oil pressure sensors, Oil temperature sensors, Oxygen sensors, PCV valves, Power steering pressure switches, Radiator fan switches, Solenoids, Spark plug wires, Spark plugs, Starter motors, Throttle position sensors (TPS), Transfer case switches, Transmission oil pressure sensors, Turn signal flasher relays, Tyre pressure sensors (TPMS), Vehicle speed sensors, Voltage regulators, Wiper switches.
A/C pressure switches
What it is: They monitor refrigerant pressure and switch the compressor on or off, protecting it from running without refrigerant or at excessive pressure.
Where it is fitted: On the A/C lines, on the receiver-drier or accumulator in the engine bay.
Signs of wear: The compressor will not engage although the system is charged, or it cycles on and off too often.
Did you know: Many of these switches sit on a valve, so they can be replaced without recovering the refrigerant – check before booking an A/C service.
ABS sensors
What it is: They measure the speed of each wheel so the ABS unit can stop the wheels from locking under braking. Traction and stability control use the same signal.
Where it is fitted: At the wheel hubs or steering knuckles, or – on older pickups with rear-axle ABS – in the differential housing.
Signs of wear: ABS warning light, traction control not working, brake pedal pulsing at low speed.
Did you know: Often the fault is not the sensor but rust under it or on the tone ring – clean the mounting bore before fitting a new one so the air gap stays correct.
Air bag clocksprings
What it is: A coiled ribbon of wires that connects the parts in the rotating steering wheel – air bag, horn and buttons – to the car's wiring.
Where it is fitted: Behind the steering wheel, on the steering column.
Signs of wear: Air bag warning light, horn or steering wheel buttons not working, cruise control unresponsive.
Did you know: Centre the clockspring before fitting and never turn the wheels with the steering wheel removed – otherwise it will tear on the first full turn.
Blower motor resistors
What it is: They set the speed of the heater blower by limiting the current to its motor.
Where it is fitted: In the heater housing, in the airflow next to the blower motor, usually behind the glovebox or under the dashboard.
Signs of wear: The blower works only on the highest setting, or some speeds do not work.
Did you know: The top speed usually bypasses the resistor, so it still works with a burnt resistor; if a new resistor fails quickly, check the blower motor.
Camshaft position sensors
What it is: They report camshaft position so the computer knows which cylinder is on its compression stroke – the basis for injection and ignition timing.
Where it is fitted: On the cylinder head, timing cover, or in the synchroniser that replaced the distributor.
Signs of wear: Hard starting, stalling, hesitation and a P0340 or related fault code.
Did you know: The cam and crank sensors work as a pair – when the computer reports a correlation fault between them, check the timing chain or belt too.
Shop — Camshaft position sensors
Camshaft synchronisers
What it is: A part that replaces the distributor on some Chrysler and Jeep engines: it houses the camshaft position sensor, and on the Jeep 4.0 it also drives the oil pump.
Where it is fitted: In the engine block, where the distributor used to sit.
Signs of wear: Check engine light with a cam sensor code, hard starting, squealing or oil leaking from the housing.
Did you know: The synchroniser must be indexed correctly to cylinder number one – fitted in the wrong position it causes fault codes and poor running even when new.
Coolant temperature sensors
What it is: They measure coolant temperature. The computer uses it for cold-start fuelling and fan control, and the gauge shows it to the driver.
Where it is fitted: In the cylinder head, intake manifold or thermostat housing, in contact with the coolant.
Signs of wear: Hard starting, high fuel consumption, black smoke, the fan never runs or runs constantly, erratic temperature gauge.
Did you know: Many older cars have two sensors, one for the gauge and one for the computer – make sure you replace the right one.
Shop — Coolant temperature sensors
Crankshaft position sensors
What it is: They measure crankshaft position and speed. Without this signal the engine will not start, because the computer does not know when to fire the spark and injectors.
Where it is fitted: In the engine block or on the bellhousing, at the flywheel or crankshaft pulley.
Signs of wear: The engine cranks but will not start, or stalls when hot and restarts only after cooling down; the rev counter stops working.
Did you know: Some sensors for Chrysler engines come with a paper spacer on the tip that sets the air gap – do not remove it before fitting.
Shop — Crankshaft position sensors
Cylinder head temperature sensors
What it is: They measure the temperature of the cylinder head metal rather than the coolant. Some Ford engines use them as the main engine temperature sensor.
Where it is fitted: Screwed directly into the cylinder head.
Signs of wear: Wrong temperature readings, hard starting, high fuel consumption, engine going into limp mode.
Did you know: Because they read metal temperature, they detect overheating even after coolant loss, when a normal sensor has nothing left to measure.
Shop — Cylinder head temperature sensors
Fan control modules and relays
What it is: They control the electric radiator fan, switching it on or setting its speed on command from the computer.
Where it is fitted: On the fan shroud, in the engine bay relay box or near the radiator.
Signs of wear: The fan does not come on, runs at one speed only or keeps running after shutdown; the engine overheats in traffic.
Did you know: A worn fan motor draws too much current and can burn out a new module – make sure the fan spins freely.
Shop — Fan control modules and relays
Fuel injectors
What it is: Computer-controlled valves that spray a metered amount of fuel into the intake manifold or cylinder.
Where it is fitted: On the fuel rail, in the intake manifold or in the cylinder head.
Signs of wear: Misfires, rough running, higher fuel consumption, fuel smell, hard starting.
Did you know: Always fit new O-rings and wet them with clean engine oil so they are not damaged when pressed in.
Fuel pressure regulators
What it is: They keep fuel pressure in the rail constant and return excess fuel to the tank.
Where it is fitted: On the fuel rail or in the fuel pump module inside the tank.
Signs of wear: Hard starting after standing, black smoke, fuel smell, fuel pressure too high or too low.
Did you know: If there is fuel in the regulator's vacuum hose, the diaphragm is leaking and the regulator must be replaced.
Shop — Fuel pressure regulators
Fuel pressure sensors
What it is: They measure fuel pressure in the fuel rail so the engine computer can meter fuel and control the pump.
Where it is fitted: On the fuel rail at the engine or on the fuel line.
Signs of wear: Hard starting, hesitation under acceleration, stalling and fuel pressure fault codes.
Did you know: In returnless fuel systems this sensor decides how fast the fuel pump runs, so a faulty one can mimic a weak pump.
Fuel pump driver modules
What it is: An electronic driver that powers the fuel pump and controls its speed on command from the engine computer. Found mainly on Fords with returnless fuel systems.
Where it is fitted: Usually on the frame or underbody, near the fuel tank or spare wheel.
Signs of wear: No start or stalling while driving, cutting out under load, fuel pump circuit fault codes.
Did you know: Mounted under the car, the module often fails from corrosion of its case and connector – protect the contacts and check the mounting when replacing it.
Shop — Fuel pump driver modules
Fuel pumps
What it is: Electric pumps that deliver fuel from the tank to the fuel rail at the right pressure.
Where it is fitted: Usually inside the fuel tank, as part of a module with the fuel level sender.
Signs of wear: Hard starting, loss of power under load, stalling, a whining noise from the tank.
Did you know: Fuel cools the pump, so frequent driving on reserve shortens its life; replace the inlet strainer at the same time.
Glow plugs
What it is: They heat the combustion chamber of a diesel engine, making cold starts easier and reducing smoke after starting.
Where it is fitted: Screwed into the diesel cylinder head, one per cylinder.
Signs of wear: Hard cold starts, white smoke and rough running just after starting, glow plug warning light.
Did you know: Cummins engines in Rams have no glow plugs – they use an intake air grid heater instead.
Idle air control valves (IAC)
What it is: They regulate the air bypassing the closed throttle so the computer can keep a steady idle, even with the A/C or lights switched on.
Where it is fitted: On the throttle body or intake manifold.
Signs of wear: Hunting or high idle, stalling when coming to a stop, hard starting.
Did you know: Carbon build-up in the throttle body and valve passage causes similar symptoms and cleaning often helps; after replacement or a battery disconnect the computer must relearn the idle.
Shop — Idle air control valves (IAC)
Ignition coils and distributors
What it is: The coil turns battery voltage into the high voltage needed to fire the spark plug. On older engines the distributor routes that spark to each cylinder in turn.
Where it is fitted: Coils sit on top of the plugs, in a coil pack on the engine, or next to the distributor, which is driven by the camshaft from the block or cylinder head.
Signs of wear: Misfires, jerking under acceleration, rough idle and a lit check engine light.
Did you know: With coil-on-plug systems, swap the suspect coil with a neighbouring cylinder: if the misfire code follows the coil, the coil is at fault.
Shop — Ignition coils and distributors
Ignition lock cylinders and switches
What it is: The lock cylinder that takes the key and the electrical switch that powers the wiring and the starter.
Where it is fitted: In the steering column or on the dashboard.
Signs of wear: The key is hard to turn or will not come out, warning lights flicker, the engine cuts out while driving, the starter does not respond.
Did you know: A heavy keyring hanging from the key wears the ignition over time and can even turn it off while driving.
Shop — Ignition lock cylinders and switches
Intake air temperature sensors
What it is: They measure the temperature of air entering the engine. Cold air is denser, so the computer adjusts fuel delivery.
Where it is fitted: In the air filter box, intake duct or intake manifold; sometimes inside the MAF sensor.
Signs of wear: Rough running, hard starting, higher fuel consumption, check engine light.
Did you know: On many cars this sensor is part of the MAF sensor – check before ordering it separately.
Shop — Intake air temperature sensors
Knock sensors
What it is: They pick up the vibration typical of engine knock. The computer then retards the ignition to protect pistons and cylinder heads.
Where it is fitted: Bolted to the engine block; on some V8 engines, such as GM, under the intake manifold.
Signs of wear: Loss of power, higher fuel consumption, check engine light, metallic pinging under load.
Did you know: The sensor must be tightened to the correct torque – too tight or too loose and it misreads vibration.
Light switches
What it is: The switches the driver uses to turn on exterior and panel lights; depending on the model, this group also includes brake light switches.
Where it is fitted: On the dashboard by the steering wheel, on the column stalk or – for brake lights – at the brake pedal.
Signs of wear: Lights will not turn on or off, one function does not work, the switch gets hot or feels loose.
Did you know: Before replacing the switch, check fuses, relays and bulbs – cheaper and more common causes of lights not working.
Manifold runner control valves
What it is: They operate flaps in the intake manifold, changing the air path with engine speed to improve low-end torque and top-end power.
Where it is fitted: On the intake manifold, linked to the flaps or a rod.
Signs of wear: Loss of power in part of the rev range, check engine light with a runner control code, rattling from the manifold.
Did you know: Some faults are not the valve itself but seized flaps or a broken linkage in the manifold – check them before buying.
Shop — Manifold runner control valves
MAP sensors
What it is: They measure intake manifold vacuum, which the engine computer uses to calculate engine load and fuel delivery.
Where it is fitted: On the intake manifold or throttle body, sometimes on the firewall connected to the manifold by a hose.
Signs of wear: Higher fuel consumption, black smoke, hesitation, rough idle and a check engine light.
Did you know: Before replacing the sensor, check its vacuum hose – a cracked or loose one causes the same symptoms.
Mass airflow sensors (MAF)
What it is: They measure the amount of air drawn into the engine, which the computer uses to set fuel delivery.
Where it is fitted: In the intake duct between the air filter and the throttle body.
Signs of wear: Hesitation, loss of power, stalling after start, rough idle, higher fuel consumption.
Did you know: Never touch the sensing element; a dirty one can sometimes be revived with dedicated MAF cleaner, and an over-oiled air filter can contaminate it.
Shop — Mass airflow sensors (MAF)
Neutral safety switches
What it is: They tell the car which position the automatic gear selector is in. They allow starting only in P or N and switch on the reversing lights.
Where it is fitted: On the automatic transmission case, at the selector shaft or lever.
Signs of wear: No start in P or start only in N, reversing lights not working, wrong gear shown on the dash.
Did you know: On many Chrysler automatics the switch screws into the case, so fluid may run out when you remove it – have a drip tray ready.
Shop — Neutral safety switches
Oil pressure sensors
What it is: They measure engine oil pressure and send it to the gauge or warning light, warning of a drop in lubrication that could destroy the engine.
Where it is fitted: Screwed into the engine block, usually near the oil filter or oil pump.
Signs of wear: The gauge reads zero or jumps while the engine runs fine, the warning light flickers, or oil seeps around the sensor.
Did you know: Before assuming the engine has lost pressure, check it with a mechanical gauge – a faulty sensor is a far more common cause of bad readings.
Oil temperature sensors
What it is: They measure engine oil temperature. The computer uses it, among other things, for variable valve timing and oil life monitoring.
Where it is fitted: In the engine block, oil pan or oil filter housing.
Signs of wear: Wrong gauge reading, check engine light, oil leaking at the sensor.
Did you know: On cars with an oil life monitor, a faulty sensor can upset the service reminder.
Shop — Oil temperature sensors
Oxygen sensors
What it is: They measure oxygen in the exhaust so the computer can keep the air-fuel mixture right. The sensor after the catalytic converter checks its efficiency.
Where it is fitted: In the exhaust manifold or exhaust pipe, before and after the catalytic converter.
Signs of wear: Higher fuel consumption, check engine light, rough running, failed emissions test.
Did you know: New sensors usually come with pre-coated threads – do not add other grease, and avoid silicone sealants near the sensor, which poison it.
PCV valves
What it is: A valve in the crankcase ventilation system that routes crankcase gases into the intake to be burned.
Where it is fitted: In the valve cover or on the hose between the crankcase and the intake manifold.
Signs of wear: Oil leaks past seals, rough idle, higher oil consumption, whistling from the engine.
Did you know: Simple test: shake the removed valve – if it rattles, it is not stuck; a clogged valve builds crankcase pressure and pushes oil out past the seals.
Power steering pressure switches
What it is: They tell the engine computer when power steering pressure rises during full lock, so it can raise the idle and keep the engine from stalling.
Where it is fitted: On the high-pressure power steering line or on the pump.
Signs of wear: The engine dips or stalls when turning the wheel at standstill, or fluid leaks from the switch.
Did you know: Stalling while parking is a classic symptom of this switch, not necessarily of a failing power steering pump.
Shop — Power steering pressure switches
Radiator fan switches
What it is: A thermal switch that turns on the radiator fan once the coolant reaches a set temperature.
Where it is fitted: In the radiator or thermostat housing, in contact with the coolant.
Signs of wear: The fan does not come on and the engine overheats in traffic, or the fan runs all the time.
Did you know: On simple two-wire systems you can bridge the switch connector – if the fan starts, the switch is at fault.
Solenoids
What it is: Electromagnetic valves that open or close the flow of oil, fuel, air or vapour on command from the computer. Most often they control automatic gear changes, valve timing or fuel tank venting.
Where it is fitted: In the transmission, on the engine or in the fuel vapour system, depending on their job.
Signs of wear: No or delayed gear changes, transmission limp mode, rough engine running, solenoid circuit fault codes.
Did you know: Transmission solenoids often stick because of dirty fluid, so change the fluid and filter when replacing them.
Spark plug wires
What it is: They carry high voltage from the coil or distributor to the spark plugs.
Where it is fitted: Between the coil or distributor and the spark plugs, along the engine.
Signs of wear: Misfires, stumbling in damp weather, crackling or sparks visible in the dark.
Did you know: Replace the whole set and route the wires in their original holders – leads of consecutive cylinders laid side by side can induce crossfire, and wires touching the exhaust manifold burn quickly.
Spark plugs
What it is: They create the spark that ignites the fuel-air mixture in a petrol engine's cylinder.
Where it is fitted: Screwed into the cylinder head, one (sometimes two) per cylinder.
Signs of wear: Hard starting, misfires, loss of power, higher fuel consumption.
Did you know: On Ford 4.6 and 5.4 three-valve engines the two-piece plugs are known to seize and break – remove them carefully with the proper tool.
Starter motors
What it is: An electric motor that turns the crankshaft when starting until the engine runs on its own.
Where it is fitted: Where the engine meets the transmission, engaging the flywheel.
Signs of wear: Only a click, slow cranking, grinding, or the starter keeps running after the engine starts.
Did you know: Before replacing the starter, check the battery and ground cables – a poor ground gives exactly the same symptoms.
Throttle position sensors (TPS)
What it is: They tell the engine computer how far the throttle is open, i.e. how hard the driver presses the pedal. Fuel delivery and, on automatics, shift points depend on it.
Where it is fitted: On the throttle body, on the throttle plate shaft.
Signs of wear: Stumbling or a flat spot when accelerating, unstable idle, poor automatic shifting.
Did you know: On newer cars with electronic throttle the sensor is often built into the throttle body and cannot be replaced separately.
Shop — Throttle position sensors (TPS)
Transfer case switches
What it is: The switch the driver uses to select drive mode (2WD, 4WD, low range), or a sensor reporting the engaged mode to the computer.
Where it is fitted: On the dashboard or centre console; the position sensor sits on the transfer case.
Signs of wear: 4WD or low range will not engage, mode lights flash or show the wrong mode.
Did you know: Transfer cases like regular use – engaging 4WD now and then, even out of season, keeps the mechanism from seizing.
Transmission oil pressure sensors
What it is: They report hydraulic oil pressure to the automatic transmission controller, which uses it to time and smooth the gear changes.
Where it is fitted: In the automatic transmission case, on the valve body or housing.
Signs of wear: Harsh shifts, no upshifts, or the transmission dropping into limp mode.
Did you know: On Chrysler RE-series automatics a separate sensor reads governor pressure, and its failure can mimic a serious transmission fault.
Shop — Transmission oil pressure sensors
Turn signal flasher relays
What it is: A relay that switches the turn signals and hazard lights on and off in rhythm.
Where it is fitted: Under the dashboard, by the steering column or in the fuse box.
Signs of wear: Indicators do not flash, stay lit or flash too fast.
Did you know: Fast flashing usually means a blown bulb; after switching to LED bulbs you need an LED-compatible flasher.
Shop — Turn signal flasher relays
Tyre pressure sensors (TPMS)
What it is: They measure the pressure in each tyre and send it by radio to the car, which warns the driver about pressure loss.
Where it is fitted: Inside the wheel, usually as part of the tyre valve.
Signs of wear: The TPMS light stays on despite correct pressures, or one wheel shows no reading – often when the built-in battery runs out.
Did you know: US-market cars usually use a different TPMS frequency than European ones, so the car's market version matters; a new sensor usually needs a relearn.
Shop — Tyre pressure sensors (TPMS)
Vehicle speed sensors
What it is: They measure road speed from the output shaft of the transmission or transfer case. The speedometer, cruise control and automatic transmission all use the signal.
Where it is fitted: On the transmission or transfer case, sometimes in the axle.
Signs of wear: Speedometer dead or erratic, cruise control dropping out, poor automatic shifting.
Did you know: After a tyre size change the speedometer reads wrong – older cars correct it with a different drive gear, newer ones by reprogramming the computer.
Voltage regulators
What it is: They keep charging voltage steady regardless of engine speed, protecting the battery and wiring from under- and overcharging.
Where it is fitted: Inside or on the alternator, or as a separate unit in the engine bay on older cars.
Signs of wear: Charging warning light, flat battery, dimming or over-bright lights, blowing bulbs.
Did you know: On many Chryslers the engine computer regulates charging voltage, so a separate regulator is found mainly on older models.
Wiper switches
What it is: The switch the driver uses to turn on the wipers and select speed, intermittent mode and washer.
Where it is fitted: On the steering column stalk, on some models on the dashboard.
Signs of wear: Only some speeds work, intermittent mode or washer dead, wipers switching on by themselves.
Did you know: If the wipers do not return to the park position, the park contact in the wiper motor is usually to blame, not the switch.
Where to next
- Catalogue: electrical parts and sensors — choose your make, model and generation.
- Parts by VIN — we will check the fit for your car.
- Parts guide — other systems.
We sell aftermarket replacement parts, not genuine parts from vehicle manufacturers. Descriptions are general — check the fit for your vehicle by OEM number or VIN.