Strange electric problem 99 Corolla

[mikevw]

I have a short in my car's system somewhere but it has unusual symptoms

I have a volt/ohmmeter connected to each battery connector (plus and minus) with the battery disconnected. There is partial continuity when the car is turned off (partial short). When I turn on the ignition all the way, the meter indicates complete shorting. When I release the key, the meter reading gradually lowers, like a capacitor is discharging. If I hold the ignition on longer, it takes longer for the meter reading to come back down.

Here's the additional info:

There was a headlight switch problem - the left blinker wouldn't come on when I pulled down on the switch handle unless I did it several times. I had replaced the flasher so the switch was apparently the culprit. I didn't get to working on it at that time.

Then, after a couple of months, the headlights would only come on during the day with the running light relay active, but not switch on at night manually or otherwise. I found the post about making a ground connection from the DRL relay (near the radiator) to the engine block. This seemed to work initially, but then another problem came up - a short. The car electric system seemed dead. I disconnected the ground wire from the relay - no change.

I figured this was due to the headlight/blinker switch and I got to installing a new one. I connected the battery and initially the car beeper went off when I turned the key and had the door open, then nothing. I disconnected the battery and hooked up my meter and discovered the strange continuity of the short.

I've checked to see if disconnecting the ignition or the washer switches behind the steering wheel would make a difference, but the partial continuity (short) is still there with no dip in the meter reading.

Are there any clues about how to narrow down a search for the culprit based on this description?

Thanks for any help.

[finkle1359]

Hello,
I will take a stab at it
From the sounds of it what you are seeing with the ohmmeter is normal. The ECU will use a little bit of power at all times. Items like the key less entry, security, etc. use power all the time no matter the ignition position.

I had to do this with a couple of old winter beaters that had electric issues. Hook up the battery (assuming its a good battery and fully charged). Go out and buy an ammeter. Test the circuits by taking out fuses and running lead wires between the circuit and the meter. If you find the radiator fan circuit is using 3 or 4 amps when off, you found your problem.

Does the car start as is, or is it completely dead?
Not that it fails often, but the signal for the turn signals has to go through the hazard switch, might be worth a second to check the switch.
If the car is dead, it sounds like a battery, fuse, or relay. It doesn't make sense that from installing the switch would make it not start. If the headlight switch shorted out, the fuse should have blown, but the car should start. Let us know what you find.

[mikevw]

Thanks for the detailed info - I did have the power completely die after initially rigging the ground wire from the DRL running lights relay to the engine block, -this was initially successful bringing the headlights on and engine running.

It was odd because I was all ready to go, and then the car wouldn't start - totally dead after trying to restart it. I disconnected the DRL ground rig at this point, but the car was dead. This was still with the old switch in. After putting in the new switch, the ignition beeper worked but the engine wouldn't turn over. Then after trying a few times, everything was dead again and I disconnected the battery (apparently it was shorting). The battery is now low at about 9 volts, but isn't the partial continuity abnormal between the battery connection cables with the battery disconnected?

I'll meanwhile see if the battery can be recharged.

I'll get into the details you mentioned. Thanks

[finkle1359]

HMMMMM,
I wonder if it is all related to the battery. This is what I'm thinking of right now. I have a curse on me that all cars I own need new batterys. I have had 2 that would radomly short themselves out and drop to almost no power. It would power the dome lights fine, but as soon as I would start it, it would go dead. After a few minutes everything would be fine. Rule out the battery first.

2nd Hypothesis:
When you put on the ground wire, something started to drain the battery or the battery itself started to short. When you disconnected the battery to test it, it had a bit of time to re-charge itself, so when you hooked it back up with the new switch, you had some power for a short time, and then it was dead.

For something to drain the battery down to 9 volts that fast, it should have blown a fuse. Unless it was before the distribution block, like the insulation rubbing off the main power or starter wire. Both of these have nothing to do with the headlight circuit, so thats sort of confusing, what if anything the two have to do with each other. The headlights are fused, so if they shorted out, it should have blown something.

If the partial continuity worries me: short answer no, long answer, maybe. I know the ECU by itself uses a few miliamps at all times, but that's at 12v The multimeter puts out closer to 3v as a test signal. I don't know if the ECU would even be able to use power at 3v, or if it would appear as an open circuit. I would start by pulling some of the fuses and see if the continuity drops to 0. Try the ECU and radio fuses first and see what happens.

When you get the ammeter, hook it up first too the main battery cable and see how much its pulling when off. Anything over .5 amp or so would be cause for alarm. More likely closer to .1 amps.
Let me know what happens

[mikevw]

thanks for the extra info! I'll get into it over the next couple of days and post an update of any discoveries. Thanks again.

[KeMBro2012]

You'd be surprised what a battery can do. The 2000 I've kept mentioning I was buying (bought it last night!!) had a rough idle issue that I was attributing to a bad coil pack. Since I have a nearly new battery in my 99, I wanted to keep that one when I sell it, so I swapped batteries. The rough idle problem followed.

Grab an appropriately sized battery out of another car, or go buy a new one, and see if the problem fixes itself.