When you are diagnosing a problem in your cars charging system it is very easy to overlook the possibility of bad battery cables.
If a cable is bad then you can have a range of problems that make it seem that other components are causing a problem. This can prolong your diagnostics and you may end up replacing items that are still good.
Battery cables are made of stranded wires that have an appropriate connector to fit your battery, alternator and starter.
Your Negative Battery Cable is connected directly to ground on your cars frame. This allows any device from your radio to lights or engine to complete the path back to the battery negative terminal simply by being mounted to the frame, using a ground strap from the device to the frame or body or getting its ground at the fuse box to the frame.
Your Positive Battery cable can come in two or more types.
The first type is the simplest and is a single wire that runs from your battery to your starter solenoid. From the solenoid terminal on the starter a wire will run to your accessories and charging system.
The second type runs from your battery positive to a relay on your firewall. From there a second large cable is sent to your starter and other smaller cables are used to connect your alternator feed and accessories / fuse box.
Another type of cable may use two smaller wires that connect to your starter and your alternator output for charging.
The newer your vehicle the more complex this is likely to be and this has more to do with bad engineering then the need for more complex wiring.
Common Problems With Car Battery Cables
The most common problem with your car’s battery cables is a loose or corroded connection.
This is a very easy fix and only requires that you remove the cable clamp from the battery and clean the connection well.
Terminal Cleaners are available at most auto supply stores for under $5 and will have a brush end that can clean inside the cable connector and a brush in a cap that will fit over your battery terminal to allow cleaning.
If your terminal is loose and this can happen from over cleaning a terminal or from purchasing a battery that does not match your cable correctly then you can install a sleeve insert which will provide better contact between the cable and the battery terminal when you tighten it.
Sometimes you will get suggestions that you need to cut off and replace the connectors on your cable. This is a very last resort and will often result in bad connections. If your battery cable connector is in good condition then there should be no need to do this.
Using an Ohm Meter to check for bad Terminal Connections
With the vehicle off and terminals connected you want to use your probe ends to touch the battery cable connector and the inside terminal. If there is any loss across this connection you definitely need to make a repair or clean the connection.
If your Ohm Meter is pinned then you still may have a connection that acts up when the car warms up. Do a visual inspection and clean the connections if you are having problems and then recheck with your ohm meter making sure there is no loss across the connection.
If your cable wire is exposed where it is crimped to your connector also check between the terminal on the battery that it is connected to and the cable end that is past the connector end.
Corroded Battery Cables
Internal corrosion of your battery cables is also common on older vehicles and it is also relatively difficult to diagnose.
Often what happens is acid from your battery will enter the cable at your connector. It will travel half way through the cable and begin to corrode it from the inside. Unfortunately since you can not visually inspect the cable you may think it is fine but it could cause a variety of different intermittent problems until it fails completely.
The best way to check for a internally corroded battery cable is to pull the wire and do an Ohm meter check however that is not usually possible or it is difficult to perform.
Another option is using extended tester cables and simply removing the ends from the battery and starter or other connector and keeping the wire in place but not connected.
The final test you can run is doing a reverse circuit test where you do not remove the cables from the devices they are connected to and then test between the battery terminal and the device. Positive output on your alternator and your positive battery terminal and also with other connections. This can often give you bad results but if you find an open or large drop it may be an indicator to pull the connectors and do the test right.
Final Note
Battery Cables not only provide needed starting amps and power for your accessories when your car is not running but they also complete the circuit of your alternator while the engine is running. For this reason you may find that poor connections or corroded wires can cause intermittent or false diagnosis for repairs.
A bad cable that is not checked can easily end up with you replacing a number of different charging components.
In a personal case an internally corroded cable left me somewhat stranded in the Winter a few hundred miles from my home with no parts or repair shop in sight.
Connecting an emergency jumper cable from the terminal of the battery to the ground of the cars frame helped me get through a tight situation until I could get home.