Checking Leads and Connection

Many faults in the electrical system are the result of faults in the leads and connections. These faults arise most often through interference from electrical systems or from mechanical or chemical effects.

When incidental faults occur, they are often in leads or connections. Check as suggested below.

Approach
- Check connections visually.
- Check resistances of contacts and leads.
- Check for open circuit.
- Check for shorts to ground.
- Check shorting between leads.
- With incidental faults, measure the resistance of contacts and leads.

Check connections visually




When carrying out measurements and tests. carry out a visual check where connectors are undone.

Checks:
- Look for corrosion which may affect the contact in the connections.
- See that the connecting pins are intact and that the copper wires are well connected to the pins.

Resistance in leads, contacts and connections
The resistance of leads, contacts and connections should actually be 0 ohms, but a certain resistance is always present as a result of poor assembly of leads, corrosion on connectors and wear and tear. If resistance becomes too large, functional disturbances will arise.

Checking intermittent faults




- Shake leads gently and pull gently on connections while measuring in order to locate intermittent faults.
- Test with a spare pin that a socket is making good contact and that the socket remains in place if you pull gently on the pin.

Measuring with an ohmmeter




- Ignition off.
- Remove battery negative lead.
- Take measurements with the ohmmeter between the ends of the lead.
Before commencing measurement, check that the ohmmeter shows 0 ohms when the probes are shorted together. Shake the lead gently and observe the reading on the meter.

The ohmmeter should not show more than a few ohms in a circuit with an acceptable standard of contacts and connectors.

Breaks in the circuit




Breaks in the circuit are revealed when some function fails to work. Chafed and worn leads, together with connections that have worked loose, are the most common reasons for faults.

Check:
- Ignition off.
- Disconnect negative lead from battery.
- Remove contacts from both ends of the lead.
- Measure between the ends of the lead with an ohmmeter.
The ohmmeter should show 0 ohms when a lead has no break.

Shorting to ground




A short between a live lead in a circuit and ground is revealed most often by a fuse blowing when the lead becomes live or by a failure in some function.

Checking for short circuit with an ohmmeter




- Ignition off.
- Disconnect the battery negative lead.
- Remove any blown fuse.
- Remove any connected components.
- Connect an ohmmeter between ground and the lead to be tested.
If the meter shows infinite resistance when no components are connected, there is no short.
If the meter shows low resistance, about 0 ohms, the lead is shorted to ground.

Shorting between leads




A short between leads does not always lead to a blown fuse. The fault is most often revealed by some function not working.

Check:
- Ignition off.
- Disconnect the battery negative lead.
- Measure between the suspect leads with an ohmmeter to see if there is a short.
The ohmmeter should read infinite resistance when measuring between leads which are not linked to each other in the circuit.

Contact resistance, corrosion
Resistance in contacts, leads and connections should actually be 0 ohms. However there is always some resistance as a result of corrosion in the leads and also wear and tear.

If the resistance becomes too high, interference will arise in the function. The extent of resistance before interference is caused varies with the load on the circuit. As a rough guide, it should be a few ohms.

Checks
- Check connections visually.

Cleaning pins and sockets






NOTE: Rust-dissolving spray or grease must not be used on any of the oxygen sensor contacts.


- Disconnect the battery negative lead. Spray rust solvent 1161034-2 on the disconnected contacts.
- Blow dry with compressed air.

Greasing sockets


NOTE: Do not fill the protective covers with grease.





- Squeeze grease 1161417-9 into the sockets straight from the tube.
- Check that the openings are filled in all sockets.




- Test with a spare pin that the socket is making good contact and that the socket remains in place if you pull gently on the pin.