How do you check for a draw on a car. I know it is with a multi meter and neg cable.?

Answer 1

With the key off, loosen then remove the neg cable, then touch it back to the neg post. With you meter on the 10 amp scale, put the neg lead on the neg terminal of the batt, and the pos lead on the neg batt cable. Then separate the cable from the battery (to avoid a sudden current spike) and read the meter. Anything over a few hundred milliamps is a problem, start pulling fuses in order to isolate the draw.

Answer 2

You need a multimeter with a DC voltage scale over 18 volts.
Place the positive lead on the battery's positive post and the negative on the battery's negative post. A good battery will read 12+ volts with no current draw. (You may need to disconnect the negative cable to take this reading as many cars have a slight current draw anyway due to clocks and radio memories and such). If the voltage reading is under 11 volts-something is drawing current.
Another way is to connect an ammeter INLINE between the positive battery post and the positive cable (you have to disconnect the POS cable and put the meter inline). You need to be pretty sure that the item drawing current isn't going to exceed the meter/cable's capacity-otherwise you'll burn them up. It's not advisable to crank the starter while this test is being performed unless the meter and cables/connections are VERY heavy duty. At least as big as the battery cables themselves for the same reason.

Voltage and current are very closely related-a current draw on a battery that is not being charged by the alternator will show as a lower than normal voltage (under 11 volts-assuming the battery is good means there is an abnormal current draw).

Good battery w/engine off=11.93-12+volts.
Good battery w/engine running, accessories off=13.8-18volts depending on temperature. (Most voltage regulators are temperature-compensating).

YOU still have to locate the device drawing the current.

Answer 3

Yes use an amp meter as described above. The test light method is no good. Many newer cars will have to sit between 20 minutes to an hour to let all of the modules "time out" before you can get an accurate reading. Anything over .030amps is too much. If you have an amp probe that can clamp around the cable it's even better because you won't lose the learned values stored in the computer which can cause running problems until the computer relearns parameters.

Answer 4

hambone has it right. the other guy's method went out with the dinosaurs. there is no way to tell with with a test light how many (milli)amp draw you have. if you have a pre-1980 car, then the test light is ok. otherwise, with all of the computers/ modules, etc that could potentially keep a draw on these modern cars, you need real numbers, like a multimeter will tell you.when you look at a test light, there is no way to tell how much current is flowing thru it.

Answer 5

i own a repair shop,and i,ll tell you exactly how to do this,you remove the negative battery cable from the battery,then hook a 12 volt test light to the cable ,and then hook it up to the negative post,now you have whats known as a bridged connection,now open a car door and if you see the light comes on you have it hooked up right,,if it comes on as soon as you hook it up that means there is something on in the car,make sure you don't have the key on,once you get it all hooked up,you can start pulling fuses or unplugging things to find the draw on the battery,it may take a while but you,ll find it,good luck with it,i hope this help,s.