Alternator Draining Battery

Afternoon all, I have been a long time reader but this is my first post. I have a 95 Tacoma V6 that has an electrical issue I can't seem to track down. When the truck is off I have a parasitic draw of about .4A. This goes away if I remove the Alt-S Fuse, Alternator Fuse, or disconnect the wires running to the alternator. I assumed it was a bad alternator so just bought a new one and installed it, however, I still have the same issue with the new alternator.

Any ideas of things I should check that could cause a parasitic draw to the alternator that is not within the alternator itself?

Thanks in advance.

 

Just trace the wires there might be the smallest of cuts in the wire the is allowing voltage to be drawn. Possibly look for any arc marks as well.

 

Thanks, I will take a look and see if anything stands out. I am thinking it has to be a short or something in the wiring harness as well, or possibly the fuse box. I just had the old alternator tested this evening and it shows i is fine so I out it back in for now.

 

Alternators don't pull juice. It's a 1 way street.

 

Correct but if any of the wires insulation on the alternator circuit have be compromised there can be a very small draw from the battery

 

A shorted diode will cause a drain

Corroded plug can also cause a drain

Most other major shorts will cause circuit protection to open

 

I fist assumed a diode as well but after putting in a new (not rebuilt) alternator I have the same issue. The only curios thing was the drain was less (0.24A) with the old alternator than with the new (0.4A) which makes me think as Sperrunner mentioned I have an issue with wiring somewhere and the shiny new alternator made a better conductor. I hate to tear the wiring harness apart to trace the wires from the plug but that may be the next step...

 

For future reference, I keep one of these on hand:

$21 Innova 3721 Battery and Charging System Monitor

https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0

Less than $15, lets you get a realtime look at the charging system and the state of the battery. For an initial diagnostic...

 

I would never take the harness all apart unless you can see that it is burnt or rubbed maybe pinched some place.

Any Physical damage should be easy to see.

Any other loads on the alternator circuit I am not sure without looking

 

There is a main battery cable, and then the control harness for the alternator. If there is an internal short in the alternator itself (i.e. bad diode, internal wiring issue) then you will see a parasitic draw with the harness disconnected, but the main battery cable still connected. If the draw is caused by a control wire issue, or an ECU issue, then the draw will occur when the control harness is connected.

Where are you measuring the draw at?

 

I set the multi-meter up in series with the negative battery terminal. The draw disappears when I disconnect either the control harness or main battery cable. Also disappears when the Alt-S fuse is removed.

 

Incorrect. An internal fault in the Alternator can cause a draw.

 

Bad ground?

 

sometimes new parts are bad right out of the box.

If I understand what is going on... your battery is not holding a charge. All electrical diagnostics start with verifying that the battery is good. If I remember correctly the large wire from the alternator goes into the fuse box "Alt S" and it is on a common buss that powers up the fuse box and also goes to to the battery. I am thinking to isolate the fuse box from the charging circuit and see if it goes away. Kind of tough to figure out not being right there and with no wiring diagrahm.

 

You might start pulling fuses. Shut the door and pull any fuse that is hot when the key is off and see if the draw goes away.

 

Sorry for the delayed reply, I have been out of town for work. The battery is brand new and tests fine so I have no reason to believe it would be the issue. Was also experiencing the issue with the previous battery when I first bought the truck. Isolating the fuse box was my next thought as well but I haven't worked out exactly how to do that yet. I could simply wire the alternator directly to the positive terminal and remove the 80 Amp alternator fuse, but I am not sure how that would impact the Alt-S fuse. I have included a pic of the wiring diagram courtesy of Autozone's website (https://www.autozone.com/repairinfo/repairguide/repairGuideContent.jsp?pageId=0900c152800610de)

 

Hi there,

I have the exact same problem you are describing with my 2014 4runner. Did you ever find out the cause?

I see no update to this issue. Please would appreciate it if you fixed it and let me know the solution

 

from the toyota manual... slightly different.

I hope you can read these. As I trace out what fuses go where I will upload the appropriate diagram. The 80 amp ALT fuse feeds the ALT-s fuse which feeds the heater and tail light relays.

Is this draw at the battery post to cable or the large wire on the alt to the alt post?

 

Thank you for posting the detailed reply. The draw is somewhere between ALT-S fuse and black connector (with L IG S M signal that go to IC Regulator) which attaches to the alternator. When I remove either ALT-S Fuse or the black connector the draw goes away. Alternator diodes tested good. Alternator tested good using Toyota specified test in repair manual..

I am just perplexed what it can be. I can still drive the car without any issues with charging the battery but once I do not drive it for 3 to 4 days the battery is completely drained.

Also, I noticed whenever I plug the ALT-S fuse back in place I hear 2 or 3 relays click in the fuse box.

A little history...this issue started for me about a month ago. I was driving in heavy rain all day and came back and parked in my garage the lights started flickering and then stopped. On the same day while doing a stop on my way back I forgot that I kept my car running and accidentally tried to start it again as due to rain I could not hear the engine running.

Also another month before that I had a new windshield installed as original one cracked due to stone hitting the glass.

So now I am not sure what it is
1. Starter shot something
2. Alternator wiring connector (not the B post)
3. Windshield related (but I was driving it for 2 weeks without any issues but first time in rain when this started)

I think I am after a wild goose chase trying to figure out my electrical gremlins...

Thanks

KK

 

I always had problems with batteries draining when the vehicles sat for a week or so.

Strange as it seems when I upgraded to 1/0 welding cable on the main ground connections the problem went away in all the vehicles .

It can`t hurt .

Possible a relay coil was being energized something searching for a ground