LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

7 Amp Currnt Draw - Short Circuit Somewhere?

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Old 12-09-14, 02:49 PM
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Michael
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Originally Posted by dicer
So likely a switch is stuck on? Electrical problems can cause fires in any make and model of cars. Especially if that alternator has a problem, it has constant power ig switch on or off.
Nope, the switch is stuck OFF and it is only turned on if I need to:
1. Adjust power seat
2. Use a power lock
3. Open Trunk
4. Open fuel lid

And I know the current leak is NOT at the alternator.

This is a temporary patch and I am going to look into it to find among the list above. I had to find a way to use the car. With this type of problem, car cannot be used because the battery get drained, overnight.

I have a hunch that it is from the driver side power seat.

Last edited by Michael; 12-09-14 at 02:58 PM.
Old 12-09-14, 10:00 PM
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Yamae
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Originally Posted by Michael
Nope, the switch is stuck OFF and it is only turned on if I need to:
1. Adjust power seat
2. Use a power lock
3. Open Trunk
4. Open fuel lid

And I know the current leak is NOT at the alternator.

This is a temporary patch and I am going to look into it to find among the list above. I had to find a way to use the car. With this type of problem, car cannot be used because the battery get drained, overnight.

I have a hunch that it is from the driver side power seat.
Don't you have an intermittent problem of any door lock/unlock?
I once had it and it was causing a battery drain within a few of days. The motor inside of the actuator did not rotate fully and the contacts were not fully open/close. This was detected by the method at the FAQ. The title is, "How to check for parasitic drain with a multimeter".

Last edited by Yamae; 12-09-14 at 10:04 PM.
Old 12-09-14, 11:11 PM
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Shmee
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I would throughly inspect the trunk harness first.
I would also recheck your cig lighters and the ignition switch even though you might not think they are within the circuit.
Old 12-11-14, 05:39 AM
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"2/14, door ajar switch lubed with graphite powder"

I haven't looked at the schematic, but graphite lubricant is electrically conductive; this may be taking your battery voltage to ground through ~2ohm path. Give it a look.
Old 12-11-14, 04:29 PM
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Michael
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Originally Posted by Shmee
I would throughly inspect the trunk harness first.
I would also recheck your cig lighters and the ignition switch even though you might not think they are within the circuit.
Shemee,

Thanks for your tips. Both trunk harness and cig lighter has been checked for presents of heat and there were no heat present. 7 Amp is a lot of current and it should generate much heat.

Ignition switch that you are referring to is the switch where you inset key into to start the engine, right? I've check for any heat present but there were none. What could go wrong there? Current drain happens even without key in the ignition. I am not sure how to take the thing apart either.....
Old 12-11-14, 04:43 PM
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Michael
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Originally Posted by fixmiester
"2/14, door ajar switch lubed with graphite powder"

I haven't looked at the schematic, but graphite lubricant is electrically conductive; this may be taking your battery voltage to ground through ~2ohm path. Give it a look.
I know for fact that is not the villain for current drain because, with the manual switch off, I lose few power functions as indicated previous post and I am not losing any current. The door switch works fine without any problem.

Speaking of which the graphite lube is one of the simplest trick I've learn from this forum and had great success. I though about replacing all four switches. Front seems simple enough but the rear, I had no idea how to replace them. Cost of switches weren't that cheap either. The door ajar switch now works. Good as new.
Old 12-11-14, 04:45 PM
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Michael
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Originally Posted by Yamae
Don't you have an intermittent problem of any door lock/unlock?
I once had it and it was causing a battery drain within a few of days. The motor inside of the actuator did not rotate fully and the contacts were not fully open/close. This was detected by the method at the FAQ. The title is, "How to check for parasitic drain with a multimeter".
I read through the FAQ you've mentioned. And I've decided to use your resistance method to try to narrow down exact component. I will report afterward. Thanks.
Old 12-13-14, 10:36 PM
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Originally Posted by Michael
Shemee,

Thanks for your tips. Both trunk harness and cig lighter has been checked for presents of heat and there were no heat present. 7 Amp is a lot of current and it should generate much heat.

Ignition switch that you are referring to is the switch where you inset key into to start the engine, right? I've check for any heat present but there were none. What could go wrong there? Current drain happens even without key in the ignition. I am not sure how to take the thing apart either.....
Do not assume heat alone is the only sign of failure. While it can be a telltale sign of an issue, it can also not be as obvious to detect as some would make it out to be.

Again, start with removing the sheathing from the harness and inspect the wires on the trunk harness.
You should be using a quality DVOM to do a voltage drop test on all suspect component or a resistance check if know values are available.
Old 12-15-14, 04:35 AM
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Turns out I was reading my multimeter wrong...you have to move the lead to a different port to make a current measurement....doh!! When I use the multimeter correctly it read .01A which I can live with. The dead battery was because the door didn't close all the way and left the dome light on for a couple of days.

So no trouble found...or trouble found with the operator!

Jim
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