(Q) Other Electrical Fault Tracing

QA. Checking Cables And Connections

Many electrical system malfunctions are caused by line faults and poor connections. These are usually caused by interference from other electrical systems or mechanical or chemical damage.


QA1. Visual Inspection Of Connections






During all tests that require removal of connectors, visually check that cables are in the proper position.

Checks:
Look for oxidation, which can adversely affect contacts in connectors. Make sure that terminals are intact and copper cores are well connected to pins or sleeves.


QA2. Breaks






Breaks in cables are discovered when a function stops working. Worn or broken cables which have come loose can cause this.

Tests:
Remove connectors at both ends of cable.
Use an ohmmeter to measure the resistance in the line.
The ohmmeter should display about 0 ohm on a line without breaks.

Testing for intermiffent breaks:
Visually inspect cable according to QA1.
Shake cable lightly and pull connectors during measurement to locate cable damage.


QA3. Short Circuit To Ground






A short circuit between a supply cable and ground will most often blow a fuse when power is applied or cause an operation to fail.


Tests:





Activate all switches and sensors in the circuit and check whether the fuse blows. Remove connectors to components in the circuit so that they do not affect measurements. Connect an ohmmeter between the cable and ground. The ohmmeter should display infinite resistance if no components are connected.

Testing intermittent connection to ground:
Visually inspect cable, according to QA1.
Shake cables lightly and pull connectors gently during measurement to locate damage.


QA4. Short Circuit To Supply






A short circuit between a supply cable and ground will most often blow a fuse when power is applied or cause a function to fail.

Tests:
Measure various points in the circuit while activating switches and sensors. The reading on the voltmeter depends on the measurement location and the value of the switches and sensors. Use the wiring diagram to determine desired reading.

Use an ohmmeter to measure between suspected problem cables to check for short circuits between them. The ohmmeter should display infinite resistance between cables which are not connected in the circuit.


Test of intermiffent short circuit to supply:






Visually inspect cable according to QA1.
Shake cables lightly and pull on connectors during measurement to locate damage.


QA5. Loose Connection






A loose connection in the connectors can be caused by oxidation of pins and contacts or poor attachment of cables. A loose connection will display the same symptoms as an intermittent break in a cable.

Tests:
Visually inspect cable, according to QA1.
Shake cables lightly and pull on connectors during measurement to locate damage.



QA6. Contact Resistance And Oxidation

The resistance in contacts, cables and connections should be 0 ohm. However there will be some resistance caused by oxidation on terminals. If the resistance is too high, it will interfere with the operation of the system. The threshold for interference depends on the total impedance of the circuit, A good rule of thumb is a few ohms.

Tests:
Visually inspect connections, according to QA1.



QA7. Cleaning Of Female Contacts And Male Pins






Ignition off.
Disconnect battery minus terminal.
Spray contact cleaner, (P/N 116 1435-1 USA) onto the disconnected connector.


QA8. Greasing Female Contacts






Note: Do not fill sheath with grease.


Press grease, P/N 116 1417-9, into female contacts directly from the tube. Make sure that holes in all contact sleeves are filled. Make sure that female contact makes a good connection and holds pin by testing with a loose male pin.