Primary vs secondary ignition (10:1 attenuator, secondary pickup)

The purpose of this test is to monitor the relationship between the ignition's primary circuit and the secondary output for a distributor based ignition system.

Connection guidance

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator


Note: This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

How to perform the test

Channel A

Plug the 10:1 attenuator into Channel A on the PicoScope and plug a premium test lead into the attenuator. Fit a large black clip onto the black plug on the test lead, (negative) and an Back-pinning or multimeter probe onto the coloured connector on the test lead (positive). Fit the black clip onto the battery negative terminal and probe the coil's negative (or number 1) terminal with the Back-pinning or multimeter probe as illustrated in Figure 1.

The example waveform shows that the voltage seen during this test is relatively high and the scaling of the oscilloscope is therefore adjusted to suit. It is important that the 10:1 attenuator is used in all situations when a voltage exceeding the scopes maximumn input voltage is to be measured.

Channel B

Plug the MI074 Secondary ignition pickup into Channel B on the PicoScope, clip the lead's fly lead on a suitable earth and clip the HT clip on to the coil lead (king lead).

Warning: When attaching or removing secondary ignition pickups from damaged HT leads there is a danger of electric shock. To avoid this risk, attach and remove the secondary ignition pickup with the ignition turned off.

Figure 2 shows the Secondary ignition pickup lead connected to the distributor coil lead.

With the example waveform displayed on the screen, you can now hit the space bar to start looking at live readings.

Waveform notes

The example waveform shows the exact relationship between the ignition's primary circuit and the secondary output. The primary circuit transfers its characteristics into the secondary through 'mutual inductance' and mirrors the primary exactly.

The blue trace shown in the example is the Low Tension (LT) signal, measured from the coil's negative terminal (marked number 1). The red trace is the High Tension (HT) output voltage measured at the king lead.

A permanent or intermittent loss of the secondary picture is usually due to a failing coil or HT (High Tension) voltage tracking to earth. Losing the primary picture will result in a total loss of HT voltage.

Further guidance

Please see individual waveform topics:

  • Ignition secondary
  • Ignition primary (king lead)


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Secondary ignition pickup (capacitive with BNC)


  • 10:1 Attenuator


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Small Crocodile/Gator Clips


  • Large Dolphin/Gator Clips


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Guided test: Primary vs Secondary