Matt81

Question for guys with more experience on the C4 electrical. The battery drained down the other day on the 1988 35th I've been working on. Couldn't see that I had any lights left on, so wanting to do a parasitic draw test. Here is my issue:

1) When meter first connected inline with the battery, it shows a draw of about 2.25 amps.
2) After about 20-30 seconds, the draw slowly drains down to 0.01 amps.

I figure that is a good sign, but I know a normal car is around 25 milliamps or so at rest.

For my digital voltmeter, I have the option of a 10A test or the 200 mA test, using different leads.

Anyone know what is creating that initial high amp draw? I can hear something activating when the battery is hooked up for the test. Not a "click" like a typical relay, but something definitely energizing.

If possible, I would like to disconnect that item that energizes when the battery is connected so I can test the mA draw with my higher resolution setting.

Any help would be much appreciated.

Matt

paul1988

Hi Matt,

I know for sure on my car (also an 88) that the headlight door controller energizes when connecting the battery and tries to close the headlights. This sounds like a heavy draw since electric motors are involved.
The interior lamps (and generally the whole CTSY circuit) are also lit just after connecting the battery.

Good luck

Matt81

Thanks Paul! That nailed it. I disconnected the headlight motors and the CTSY fuse (like a dummy, I never once looked inside the car while I was doing the test - kept my eyes glued to the DVM display!). With those items removed, amp draw went to 8.6mA. Plenty good.

That is with the radio disconnected. A whole other project there.

Hot Rod Roy

The right way to do the parasitic draw is to have everything connected, so you're testing the entire system, except the under hood lamps will need to be disconnected, since you'll need to have the hood open. Close the doors and hatch. With the battery disconnected, place a jumper wire between the battery post and the battery cable, so everything receives power as is normal. Without disconnecting the jumper wire, put your multimeter cables between the battery post and the battery cable. Wait for a minute or so, until the interior lights go off. Then remove the jumper wire. Your reading will be an accurate measurement of your parasitic draw.

I get 13 mA (0.013 A) on my '84.