Abstract: An apparatus for testing an internal combustion engine is disclosed. The apparatus comprises a probe for electrical connection to at least one spark plug wire of the engine being tested. A peak hold circuit operates to store a representation of a peak firing voltage of the rectified secondary ignition signal and attenuates the stored representation at a predetermined rate over time to enable measurement of peak firing voltage. The testing apparatus is connected to a voltmeter to display a value of the peak firing voltage. Alternatively, the testing apparatus includes a display for displaying the value of the peak firing voltage. Preferably, the testing apparatus is housed in a housing of a size to be held in a user's hand, with a power supply contained therein.

Abstract: A mechanical multiplexer includes a receptacle and a removable coupling module. The receptacle includes a first and second set of receptacle contacts. The removable coupling module has a body and a first and second set of module contacts extending below the body and arranged to make electrical contact with the first and second sets of receptacle contacts, respectively, when the coupling module is inserted into the receptacle. The contacts of the first set of module contacts are electrically connected to eider the contacts of the second set of module contacts or other contacts of the first set of module contacts in a selected connection pattern.