A Practical Diagnostic Tool This is a must have diagnostic tool for any engine with a spark plug, and it can quickly and easily diagnose ignition/engine outboard motor issues or a fault in the fuel delivery system. Material The exterior of this inline spark plug tester is made of hard plastic, in addition to the internal pure copper wire made of high-voltage resistant wire which can withstand high-voltage current. The high brightness neon bulb can be used for a long time without heating up.
