When the display drops to a nominal mA draw, note the fuse/relay position number and check the vehicle’s manual. For those fuse boxes that are inside the vehicle, a tip is to lay the meter on the windshield facedown so you can see the display. If there is no joy with the fuses, start removing the relays. Locate the fuse panel(s) and start pulling out fuses one after the other, taking notice of any drop in the reading on the multimeter. The tried and tested method is to start pulling fuses to see which circuit is the culprit. It is now time to see what is causing the draw. In this instance, the threshold might be 100mA. Just note that if you have a big, modern, luxury car its added computerized systems will likely increase the natural current draw. If you see a reading of around 50mA and above on a standard car, it generally means something is drawing power and you likely have parasitic draw. If you get ‘OL’ on the screen, it means over limit and you should select a higher range.
#12 VOLT BATTERY METER MANUAL#
On manual ranging meters, you will need to select a range, usually either 2A or 200mA.
Newer, auto ranging multimeters will automatically select the correct range of a signal they pick up. Vehicle batteries put out a lot of amps due to being low voltage.
So wait a few minutes before conducting the draw test.ĬAUTION: when connected, avoid starting the engine or even turning on the headlights as this will likely blow a fuse in the multimeter. Modern car systems may ‘wake up’ when you connect a multimeter in such a fashion as it picks up the power of its batteries. Voltage, on the other hand, is measured in parallel.
#12 VOLT BATTERY METER SERIES#
Note: in order to test for current, the multimeter must be connected in series with the circuit as it needs to gauge electron flow, so to speak. Then connect the red probe to the previously disconnected negative cable of the car loom, and the black able onto the battery terminal. Plug the black probe into the common ( COM) jack input of the multimeter and the red probe into the amps (usually A) jack input. It is always best to do a parasitic draw test from the negative side so there is no chance of accidentally shorting should you test from the positive side. Pop the hood and disconnect the negative cable from the negative battery terminal. Even a key in the ignition can have systems waking up on newer cars that will initiate draw. Be sure to close all doors, turn off the radio and disconnect accessories, such as smartphones and add-on GPS devices. You should have a fully charged battery before starting – voltage would be around 12.6V for a good one. It is best to stick with a brand name, though you don’t necessarily have to go with a top branded Fluke model. You can buy fairly cheap, half-decent multimeters these days, but bearing in mind that the cheapo, no-name ones are not known for their quality or input protection. You also need a milliamp range for higher resolution to pick up minimal current draw as most faults tend to be of the trickle variety. A DMM with the ability to measure continuous current to 10A will be fine in most cases, though one rated 20A would be less prone to blowing a fuse. What You’ll NeedĪ digital multimeter is best for this test as opposed to an analog one, which is not as accurately read. In addition, any number of fancy electronics systems that are installed on newer cars could be playing up, such as your GPS or proximity key system. It could be anything from a dimming dome light staying awake or glove compartment switch sticking on, to faulty aftermarket radio or alarm wiring. A certain amount of draw is normal – in the region of 25mA (milliamps) – but if you have 100mA or more being lost, something is up. It typically happens due to a short circuit that can be tricky to pin down. The result can often lead to a flat, caused not by a faulty battery or through something obvious like the headlights being left on. On occasion, a battery may experience significant drain long after the engine has been shut off.
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