How To Check For A Draw On A Car Battery With A Test Light

Whenever you switch off your car, turn off all the lights, and shut the doors, the battery is supposed to preserve its initial state of charge. Unfortunately, that’s not always the case. Some people still wake up to a dead battery. This always begs the question as to where the charge is draining to, especially when the battery in question is new.

Well, some things, such as the audio system, may be the culprits draining your battery overnight. It’s recommended that you check for such drains, once in a while, to avoid such inconveniences.

So, how can I check for a draw on a car battery with a test light? This is an old school way of testing the parasitic drain. You can still use the method if you don’t have a multi-meter with you.

You need to connect one end of the test light to any battery terminal. The other end should be connected to the loose clamp that you unplugged from the used battery post. If the test light lights, it means that your car battery has a parasitic drain.

The simple trick should tell you that something in your car isn’t right. Something is draining your vehicle when it’s at rest. The quick procedure can’t give you the exact part that’s wasting your battery. It’s for this reason that you need to follow the process that I will provide below. By following the guide, you will be able to point out the root cause of your drain and know what to go about.

9 Steps to Do a Parasitic Battery Drain Test

1. Prepare for the Parasitic Test

When dealing with a parasitic drain, you have got to be sure that you’re picking the right readings. Therefore, you ought to prepare for everything properly. You need to do the following:

• Ensure that the test light is in excellent condition
• Turn off your car and remove the key from the ignition
• Turn off all the accessories
• Unplug devices such as phones from the sockets
• Ensure that the battery in question is charged fully. If not, add some more charge
• Lock all the doors of your car

2. Locate the Battery and Loosen One Terminal

Locating the position of your battery may seem like an obvious thing. But you must know that it’s not the same for everyone. Some people have trouble finding their battery, especially if it’s their first car. Some cars come with their batteries stuck in the trunk area, while most have their cells in the engine bay.

After you locate the battery, unscrew one of the clamps. You can use either the positive terminal or the negative terminal in this case. However, it’s recommended that you use one that is near you while you’re facing the battery. The hack prevents you from shorting the battery because you won’t have to work over another terminal.

3. Connect the Test Light

After loosening the battery clamp, the negative one, for instance, you should go ahead and connect your test light. Attach one end of the test light to the free battery terminal. The other end should be connected to the clamping cable you just unscrewed. After the connection, the test light will light, indicating that there is a power drain in your battery.

4. Locate the Car’s Fuse Box

In the engine area and under the dash, locate the fuse boxes. It’s usually black and contains the fuses to almost every component that may be draining your battery illegally. Those are the fuses you will be using to test the root of your troubles.

5. Pull Out the Fuses One by One

Next, you should go ahead and start pulling each fuse, one by one. A fuse puller can help if it came in handy. You can start with the fuses that have small amp ratings and finish with those that have the highest ratings.

After you pull out a fuse, check to see if the test light goes off. If it doesn’t turn off, replace the fuse and move to the next. If the test light doesn’t show changes with the fuse box in the engine area, proceed to the fuse box that is usually under the dash.

6. Stop When the Light in the Tester Goes Off

When the light goes off, it indicates that there is no parasitic drain. That happens when you pull off the fuse to the component that is draining your battery while the car is at rest. Therefore, once the light goes off, you have just found out your culprit.

7. Confirm What’s Running on the Affected Fuse

Confirm from the fuse box’s chart or the owner’s manual to see the component that is being powered by the fuse in question. You can as well check the wiring diagram to help narrow down the problem at hand.

8. Replace the Fuse and Flip All the Switches that Correspond to the Fuse

For example, if the fuse in question powers the radio and the power antenna, you can start by unplugging the radio switch first. If it doesn’t show any changes, repeat the same for the antenna. The trick should give you a straight answer to what’s draining your battery.

9. Repair the Problem

Once you are sure where the drain is coming from, you can go ahead and deal with the repairing. Some wastes are caused by things such as poor wiring. You can have a specialist come and address the problem if you find it hard to repair.


Often, people fall victim to battery drains. Such instances don’t go well as the empty battery can see you stranded in the middle of nowhere and with no one to help you. It’s for this reason that you are required to check what might be draining your battery now and then. Checking for a parasitic drain in your battery can be performed using a multi-meter.

However, you can still go old-school and use a test light. Explained in this article is a step-by-step guide on how you can perform the task and arrive at the specific component that is causing the drain. With this simple guide, you no longer have to be a victim or battery drains that you can’t explain.