Final answer:
A combustion analysis device can be used to test an ignition harness for suspected leakage.
Step-by-step explanation:
The test instrument that could be used to test an ignition harness for suspected leakage is a combustion analysis device. This device is commonly used to determine the carbon and hydrogen content of a sample. It consists of a test tube containing the mixture connected to a Bunsen burner, where the heat is applied to initiate the reaction.