Theory Of Operation
A circuit load test can be performed to test the ability of a circuit to carry the current required to operate a connected device. A circuit load test should be performed after a circuit has passed a resistance test using a DVOM and the circuit is still suspected of a failure.
- A single copper wire strand will carry enough current to light a test light bulb, while showing very low resistance using a DVOM.
- Some test lights are insufficient for load testing because of the very low resistance bulb being used.
- The Load Test tool listed below will require higher current flow to power the bulb; and this will test the ability of the circuit to carry a load.
- This test will indicate if the circuit being tested can carry the current required to operate a connected device.
To avoid possible serious or fatal injury, DO NOT load test any air bag/restraint system components or circuits using the procedures listed here. Refer to the appropriate Service Information for proper air bag/restraint system testing procedures.
Do not load test any circuits with components still connected to the circuit.
Depending upon the location of the circuit in question, this test may require jumper wires.
Use the wiring diagrams as a guide to trace the circuits and look for any in-line connectors where the circuit failure could occur intermittently. Look for any chafed, pierced, pinched, or partially broken wires. Look for broken, bent, pushed out or corroded terminals - clean/repair as necessary. Verify that there is good pin to terminal contact in the related wire harness connectors.
Here is an example of a simple tool you can build to test a circuit`s ability to carry a load.
The following is a list of components required to build a load test tool:
- 3156 Bulb
- 3156 Bulb socket
- Negative alligator clip with covers
- Positive alligator clip with covers
- 2 Amp mini fuse
- Mini fuse holder
- 2' to 4' of Black 16ga wire
- 2' to 4' of Red 16ga wire
- Approved back probe tool
- Shrink tubing
- Solder