Ignition cables (ignition wires)

The ignition cables are responsible for conducting the required voltage generated by the ignition coil to the spark plug with as little loss as possible.


Due to their installation position, ignition cables are subjected to high loads. At first glance, the complex inner workings of ignition cables and ignition cable harnesses are not immediately obvious. They have to perform at the highest technical level in the engine compartment, where temperatures of up to 200 degrees Celsius prevail due to catalytic converters and increasingly powerful, compact engines; electronic ignition systems produce high voltages of up to 40 degrees Celsius.000 volts. With increasing age, the brass and stainless steel contacts oxidize. The electrical resistance of the cable increases – and with it the risk of failure of the ignition coils.

Today, PVC Hypalon ignition cables no longer meet these requirements. In current vehicles, even class F ignition cables must be silicone with a temperature resistance of up to 220°C and a dielectric strength of 40.000 volt are installed. This

  • Protecting against energy loss
  • Offer optimum protection against vibrations, water, acid, oil and gasoline
  • Fulfill the highest requirements in terms of interference immunity and electromagnetic compatibility (EMC) with the appropriate connectors.

When installing new cables, make sure that they are not kinked or compressed. Above all, they should not come into contact with hot parts due to the risk of fire.

Environmental protection

Plasticizers escape from the plastics of the sheaths over time. As a result, the sheaths become brittle over time. This process can be accelerated by high temperatures and contact with oil or fuel vapors or even dissolve the plastic completely. Damage in the insulation leads to ignition voltage flowing to ground. The consequences: misfiring and rough engine running, with unburned fuel getting into the catalytic converter.

With each misfire, valuable gasoline is injected but not burned up. This significantly increases the environmental impact due to the additional consumption per kilometer alone. In addition, the unburned fuel in the catalytic converter can ignite explosively and damage it, so that the catalytic converter can no longer render the dangerous pollutants carbon monoxide, nitrogen oxides and hydrocarbons harmless and must be replaced.

Value retention

Since ignition cables are subjected to high loads, the cables should be checked regularly and replaced at the first signs of aging. Defects in the ignition system and catalytic converter usually only come to light through the legally required exhaust emission test. Regular testing is therefore an important precautionary measure that can save costs. Damage discovered in good time is less expensive to repair: replacing the entire ignition cable with plug is much cheaper than replacing a catalytic converter that has been affected by consequential damage.

Damage detection for ignition cables

The external appearance of an ignition lead can provide information about the cause of a defect in the event of damage. A precise visual inspection of the ignition cable is therefore the first step in diagnosing damage. For example, a deformed plastic sleeve indicates that the ignition cable has most likely been improperly routed in the engine compartment.

However, damage to the ignition lead is not always apparent. Externally undamaged ignition leads can be checked with a multimeter. With this important diagnostic device, the resistance of the ignition cable can be read and compared with the permissible resistances.

Replacing the ignition leads

Ignition cables in the engine compartment are wearing parts that usually reach their service life limit in quick succession. Workshop professionals therefore know: if a vehicle is of the appropriate age or has a high mileage, it is advisable to replace the entire ignition lead set right away. In addition, the components of an ignition system are complex and must therefore be precisely matched to one another. If, therefore, an ignition cable is inadvertently retrofitted with a different technology – for example, a carbon ignition cable instead of a copper one – this can lead to massive interference in the engine management system, affecting EMC and even safety-relevant electronic components.


Codies are used – depending on the type of vehicle:

  • of a mechanical ignition distributor and a distributor cap,
  • of a fully electronic ignition module,
  • A fully electronic semi-direct ignition system or. Dual spark ignition coil.

Since the ignition voltage (U) in the high-voltage range can be up to 36.000 volts, the ignition cables must be correspondingly protected against breakdown. The ignition voltage must never be allowed to penetrate the sheathing and flow to the vehicle ground, as this would lead to misfires.

Resistors are used in all ignition lead systems, although the basic aim is to achieve low-loss transmission. A look at electrical engineering makes it clear that this is not necessarily a contradiction. All electrically operated devices generate electromagnetic fields of greater or lesser strength. Although these are harmless in most cases, they can be undesirable under certain circumstances. This is the case, for example, if radio reception is disturbed. The ignition system requires optimum close interference suppression to ensure trouble-free operation of radios, communication electronics, engine or transmission control units. The assumption that resistors reduce the ignition energy and thus the engine power proves to be a mistake.

The resistors used are dimensioned in such a way that they can be neglected. The ignition lead systems offered by brand manufacturers provide the best interference suppression with optimum ignition performance. The unit for measuring the resistance (R) is ohm. For ignition leads, this value is in the range of a few thousand ohm or kiloohm. The purpose of this resistor is to reduce the disturbing electromagnetic radiation. This is achieved by limiting the current (I) through the ignition cable and at the same time ensuring that the spark plug continues to receive the required voltage (U). The mathematical formula for this is U = R * I.

Electromagnetic compatibility of the ignition leads

The ignition system consists of a coil and capacitors, also known as an "oscillating circuit" in electrical engineering terms called. Interference suppression resistors (usually 1-5 kohm) are integrated in the ignition circuit. These reduce the electromagnetic oscillations and ensure the interference-free interaction of the various devices. This is called "electromagnetic compatibility" (EMC) is called.

Ignition cables with inductive reactance have a special feature: with this design, the resistance changes depending on the ignition frequency (engine speed). Here, due to the wire coil, a greater (inductive) resistance builds up at higher speeds.

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