Safety precautions for transistor ignition system (Mercedes-Benz S-Class W126)

In the electronic ignition system, voltage reaches values of up to 30 kV. Under unfavorable circumstances, such as humidity in the engine compartment, voltage surges can break through the insulation, leading to an electric shock when touched.

• To prevent injury and/or damage to the electronic ignition system, when working on vehicles with an electronic ignition system, pay attention to the following:
• Do not touch or disconnect the spark plug wires while the engine is running or when starting.
• Disconnect ignition system wires only when ignition is switched off. When ignition is switched on, high voltage shock may be caused by shaking the distributor.
• Connecting and disconnecting measuring instrument wires (tachometer, ignition tester) perform only with the ignition off.
• Do not connect a noise suppression capacitor or test lamp to terminal 1 (-). Do not connect measuring instruments or a strobe lamp with a supply voltage of 12 V to terminal 15 of the ignition coil when the engine is running.
• Terminals 1 and 15 of the ignition coil must not be shorted to ground.
• When the engine is running, do not carry out any tests where the high-voltage wire is located away from the ground, or disconnect individual spark plug connectors.
• The high voltage test should not be performed when starting with the high voltage wire from terminal 4 of the ignition distributor disconnected.
• Before the engine is driven by the starter (for example, when checking compression pressure) or scroll by hand, turn off the ignition and the plug of the inductive sensor of the ignition distributor (green wire) and disconnect from the switch.
• The ignition coil must not be replaced with a coil of a different design. Never install an ignition coil designed for a contact ignition system.
• When heated above 80°C (varnishing, steaming) the engine should not be started immediately after the warm-up phase.
• Wash the engine only when the engine is at rest.
• When performing electric and spot welding, the battery must be completely disconnected.