johnjm22

I'm trying to track down a power drain on my battery.

When I have everything that could be drawing power disconnected or turned off, (hood light & after market audio amp disconnected, doors & hatch closed ect.) I connect my tester light between the negative terimal, and the negative cable, and the tester light illuminates:


After pulling all my fuses and disconnecting the starter and alternator, the test light stayed on, so I figured maybe Thirdgens are supposed to draw a minute amount of power even when shut off (some modern cars do). So I tried hooking up a spare license plate light, figuring it would require more power. When I hooked it up I it stayed unlit:


But I know I have the light hooked up properly because when I open the door it illuminates:


So what's this telling me? The draw on my battery, whatever it is, is just very small? Why would one light illuminate, but not the other?

What's also bizzare, is that when I first hook up the license plate test light, it will illuminate for a second, and then go out.

1986tpiiroc

I have an 86 IROC and with everything off the only parasitic drain, that is Radio memory and ECM Memory, im only pulling .18 Amps which I believe is normal for Memory on ECM and Radio.

johnjm22

Ok, so that might explain why the tester illuminates, but not the license plate bulb.

The tester is 3.5V. Would .18A be enough to illuminate it?

The license plate bulb I used is 14V .3A and 3.78 watts. So I'm guessing a small draw like .18A wouldn't be enough to illuminate it. Forgive my ignorance I don't know much about electronics.

Maybe I don't have a parasitic drain after all...

1986tpiiroc

I believe that at 3.5 volts would be enough to illuminate as its very low voltage, but a regular 12 or 14 volt bulb would not. I used my meter on the Amp side to test this as I wanted to know what I was drawing after I found my drain. It turned out I accidently left the hatch light on without knowing it. lol.

Six_Shooter

iTrader: (2)

Using lighyts to try and test for current draw is pointless. Lights don't tell yo0u a thing.

What you need is a DMM (Digital MultiMeter) to measure the current draw.

1986tpiiroc

Yes, A DMM is the best way to go when tracking down a draw or troubleshooting anything electrical in the car. If u dont have one id go and invest in one. Theyre not expensive at all unless u get a really good brand like a fluke.

whitedevilTA

iTrader: (8)

Correct me if I'm wrong, but the way you are doing it won't tell you anything. If you are attaching the test light clip to the neg post on the battery and then touching the neg cable, the battery is not grounded so the light will always light up (showing that it's a bad ground.) You have power at the positive post and nothing grounded....when a test light lights up on a ground connection it means you have a bad ground (which is obviously because the neg cable is disconnected). For an ACTUAL draw, get a multimeter and try it.

sailtexas186548

iTrader: (2)

as long as the neg cable is grounded like it is stock to the passenger fender, then the test light (best to replce with a DMM) between the neg cable and neg terminal will indicate if you car is drawing power. it should NOT draw any type of measurable power with everything shut down, other than the tiny tiny amount the pmc, radio, and alarm use to keep their memories. if you have a draw thats draining your battery, set up your light or DMM and start pulling fuses until it goes out, when it goes out you'll know which circuit is has a short and is drawing power. Then you get to go through that whole circuit to find the short. I'm having a similar problem, its a PITA

Six_Shooter

iTrader: (2)

A test light will always be on, in a case like that, even when there is a proper amount of standby current draw. Test lights will tell you nothing for current draw tests. Is the light bright or dim?

Get a DMM, and find the actual current draw.

sailtexas186548

iTrader: (2)

Do you know what the acceptable "standby" current draw is for these cars?

I'd much rather read the DMM and pull fuses, than disconnect the radio, alarm, and pcm before pulling fuses. I guess if the current draw drops when a fuse thats not on a standby draw circuit that would indicate thats the short, but if the short is in a standby draw circuit you'd need to know the stock current draw to diagnose it.

Six_Shooter

iTrader: (2)

Yes, stock acceptable current draw is < .01 amps.

I was saying that a DMM is the only way to do it, that a test light will always just be on, even when acceptable standby current draw is being pulled.

sailtexas186548

iTrader: (2)

greater than .01 Amps ?

Six_Shooter

iTrader: (2)

Less than, fat fingered that one.