A low-tension circuit is also termed the primary circuit of the ignition system. It includes the ignition switch, battery, the coil’s primary windings, and the contact breaker points present in the distributor. A fault in these components can cause the car’s engine to misfire or bring the car to a complete standstill. Checking the low-tension circuit is very easy, provided you have a multimeter available. However, If you don’t have a multimeter with you, there are other ways to check the circuit as well. Read on to find out how to check the low-tension circuit in a car’s ignition system.
Signs of Faults in Low-tension Circuit
Faults in the Low-tension circuit can be observed. Following are the signs that you should be on the lookout for before you start checking the low-tension circuit in the ignition system:
The car stalls or starts to misfire while driving.
When you turn on the ignition, the car doesn’t start at all.
The check engine light on the dashboard of your car comes on.
Your car’s engine develops a sudden decrease in fuel efficiency, which causes a strain on your pocket by increasing your fuel spending.
The engine starts overheating.
The spark plugs start to falter or burn out very frequently.
How to Check the Low-tension Circuit
Things required to Check the Circuit:
- A multimeter or tester or simple voltmeter
- A screwdriver
- A test blub
- A pair of plastic insulated pliers
Components to be Checked
The following electrical components need to be checked in a low-tension circuit in order to single out a faulty component or fault components in an ignition system:
- The battery and its leads and connections.
- The ballast resistor present in the coil.
- The coil and its leads.
- The leads attached to the distributor.
- The contact-breaker points present inside the distributor.
Checking the Low-tension circuit
Battery:
Using a multimeter, you can check the battery by placing its red probe on the battery’s positive terminal and the black one at the battery’s negative terminal.
The battery should give off a 12-volt reading on a multimeter if it is working fine. If the reading is less, you need to change it with a new battery or charge it by using a car battery charger for some time. Also, check the battery leads and connections for any signs of damage.
If you don’t have a multimeter, you can use a test bulb to check the battery, but it would only indicate the flow of current, not an exact reading of the voltage being emitted through the battery.
Also, make sure that the electrolyte level in the battery is above the battery plates. Refill if required.
Ballast Resistor:
A ballast resistor is a specially designed wire that decreases or increases the voltage coming from the starter according to the heat present in the wire. In cold weather, the ballast resistor facilitates the ignition for extra voltage, easing the strain on the battery.
You can use a multimeter to check if the resistance in the wire is accurate. Slide the multimeter on the Ohm feature to measure the resistance.
Wires and Connections:
You can visually inspect all the leads and connections for kinks and damage. For a more accurate check, you can measure the voltage in the wires attached to the coil.
By connecting the positive probe of a multimeter to the coil’s positive terminal and the negative probe to earth, you should be able to get a 12-volt reading. The reading can drop to 7 volts if the ballast resistor is attached to the coil.
If the multimeter gives no reading at all, then there is an issue in the wires as the circuit is not completed.
Coil:
To test the primary winding of a coil, you need to open the distributor first and place a card between the contact-breaker points.
Now connect a multimeter probe to the coil’s CB terminal and earth the other probe. The reading on the measuring instrument should be 12 volts. If the reading on the multimeter is zero, there is a coil breakage or a short circuit inside the distributor.
To identify if the issue lies in the coil or the distributor, you can check further by disconnecting the low-tension lead and testing again. If the reading continues to be zero, there is likely a breakage issue in the coil. Buy and fit a new coil in your car.
However, if the reading is more than 12 volts, the distributor or the low-tension lead might be short-circuited.
Distributor Leads:
Make sure the leads are tightly secured in their place. Using a multimeter or a voltmeter, check the wires in the low-tension terminal of the distributor and the terminal post of the contact-break points. Also, check the wire between the contact-breaker point and the condenser. The reading should appear at 12 volts for all the wire connections.
Condenser:
You may also want to check the condenser for any short circuits, but you will have to remove it from its mounting and check the reading on the voltmeter to determine if the current is flowing through the circuit. If the reading is 12 volts, the condenser is faulty and must be replaced. Depending on your car type, buy and fit a new condenser inside or outside the distributor.
Contact-breaker points:
To check the contact-breaker points, make sure they are assembled properly. Close the points and attach the multimeter between the coil’s negative terminal and the earth. When you switch the ignition on, the reading on the meter should be zero.
An increase in voltage might indicate a fault in points. You should clean them thoroughly and make sure they are placed accurately.
And there you go, a thorough check of the low-tension circuit. If you continue experiencing issues when turning the ignition, there might be other reasons why your car isn’t starting properly.
It is advisable to check and replace any fuses that might have blown. It would help if you also changed your old spark plugs with good quality spark plugs for better performance.
Knowing how to check the low-tension circuit can help you ensure that your ignition system is working optimally during regular maintenance checkups. You can easily spot an issue within the circuit and fix it by yourself with any help from a professional at the workshop.
