Checking Circuit Resistance or Continuity
WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
- Expect less than 2 ohms of resistance for most wiring harness circuits.
- A standard DMM ohmmeter's low-resistance resolution (approximately 0.1 ohm) limits its accurate use to circuits carrying less than approximately 5 amperes. This is because very small resistances, undetectable by a standard DMM, cause significant voltage and power loss in higher current circuits.
- A voltage drop measurement is required for higher current circuits.
- Standard DMM apply a small amount of voltage to the circuit or component to calculate resistance. As a result, these ohmmeters are very sensitive to any level of voltage present. Voltage present in the circuit will corrupt the DMM reading.
- Recommended practice: Reverse the leads and check for changes in the resistance measurement. Reversing the DMM lead connections should never change the resistance measurement (unless the circuit contains a semi-conductor).
Measurement differences when leads are interchanged at the test points indicate invalid test results.
- Recommended practice: Reverse the leads and check for changes in the resistance measurement. Reversing the DMM lead connections should never change the resistance measurement (unless the circuit contains a semi-conductor).