Is a faulty alternator causing current drain or could it be something else?

NOSTALL

MEMBER
1992 TOYOTA COROLLA
163,000 MILES

Multiamp current drain when car is off. Both battery light and brake light come on when traveling at moderate to high speed. They go off at low speed and idle and sometimes when brake pedal is pressed. Alternator charges at about 13.8 volts when checked at idle. With car turned off drain continues when output connector is pulled from alternator. Drain stops when input wire to alternator is pulled.

4 Replies

CUP1981

MEMBER
133 POSTS

Sounds as if the battery of alternator have failed, causing the brake light to come on. This is because there is not enough power to keep the system operating correctly. You need to have those tested -- most shops test them for free.

The alternator could be the source of the draw, especially since the draw goes away when the cables are disconnected. So, you could potentially kill two birds with one stone by replacing the alternator. Have it tested though before replacing it -- voltage output is only 1/3 of the testing process.

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Wednesday, September 21st, 2011 AT 10:51 PM

MMPRINCE4000

MECHANIC
8,548 POSTS

Usually when alternator goes, the BAT. Light and brake light come on.

You need to get the alt. Checked for diode and ripple.

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Monday, September 26th, 2011 AT 11:52 AM

WRENCHTECH

MECHANIC
20,761 POSTS

I wouldn't change anything until you have done some testing.
There is a procedure for finding a battery draw like that.

You will need a digital ammeter and a jumper wire with clips on the ends to do this.
First rig any door switches so you can have a door open without triggering the interior lights and unplug the hood light. Remove one battery cable and attach the meter in series between the battery cable and battery post. Take the jumper wire and also attach it the same way. Leave the jumper wire on for at least 10 minutes to expire all the automatic timers. Now remove the jumper wire and read the meter. Anything over 50ma is too much draw. The way you locate this is to start removing fuses one at a time until the meter drops to normal level. This will be the circuit with something staying on. For the alternator, you will have to disconnect the main feed wire to test that. Determine what components are part of that circuit and check them individually until the problem is isolated.

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Monday, September 26th, 2011 AT 12:23 PM

NOSTALL

MEMBER
2 POSTS

No large current drain detected when checked at service station. Alternator then proceeded to burn out while system was being checked at service station. Alternator was replaced. No more current drain.

Thanks for your help
nostall

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Sunday, October 2nd, 2011 AT 4:12 PM