Parasitic Battery Draw

Joined
Oct 17, 2019
Messages
34
Location
Washington
Gentlemen,

I come to you in a time of need. I am about to rip my hair out, and I could use any advice you can offer. Last Christmas I decided to be nice and help a lady on the side of the road, her car battery was dead. She hooked her car up and I went back to the cab of my '94 to grab something and when I did, she reverse jumped my battery. Sparks jumped off my negative terminal, but other than that nothing happened. We hooked up the battery like we were supposed to, got her started then she was on her way. That is where the nightmare started. Ever since then my truck has had a parasitic battery draw that I CANNOT figure out. Here is my list of troubleshooting points:

New Denso Alternator
New Optima Red Top battery
New Fusible Link
Wits End 2.0kW starter rebuild kit
I pulled the big 3 wire harness out, wire wheeled all of the contact points, inspected all the wiring, and then put anti corrosive on all the connectors and re-installed.
I put a multimeter in series on the negative terminal of the battery to reveal a draw of a whopping 16.1 mA. I have a cheap non-true RMS multimeter and I don't know how much I trust that reading.

I put the red top battery in the truck back in December, is it possible that the constant cycle of dying and then me jump starting the truck brought about a premature death to the battery?

Are there any other key points on the starting system harness that I should look at where something could be shorting to ground?
 
Joined
Oct 17, 2019
Messages
34
Location
Washington
^^^^

Did you pull fuses one by one to look for the circuit causing the draw?
I tried to but the truck must have sensed that I am trying to figure it out and it suddenly did not want to register on the multimeter anymore. Toyota spec is 50ma max draw so less than half seems pretty good.
 
Joined
Apr 14, 2016
Messages
1,194
Location
Oregon
Could be a bad diode in the alternator.

 
Joined
Dec 8, 2006
Messages
10,240
Location
New Jersey
Website
www.sdsysdesign.com
I put a multimeter in series on the negative terminal of the battery to reveal a draw of a whopping 16.1 mA.
16mA of quiescent draw is slightly lower than normal. Typical quiescent draw on an 80 Series is usually in the 20-30 mA range.
If your meter is accurate, then you don't have an issue with parasitic draw.
If your battery goes flat with that amount of draw, then either the battery is faulty or the alternator is not charging properly.
 

cvenom96

SILVER Star
Joined
Sep 14, 2015
Messages
472
Location
Frederick, MD
I just had a similar issue where I had a draw somewhere. Turned out after installing the new brake booster, the brake light switch was just slightly off. The brake lights would be off when I got out but the slightest vibration like wind or even a car going by was enough to trigger them at night. I'd come out in the morning with a completely dead battery. Once adjusted no problem. Long story short, once that was fixed, the static draw I measured was right at 20mA. It's either the battery or the alternator.
 
Joined
May 31, 2015
Messages
281
If all previous suggestions fail, have you checked your grounds? It’s not high on the list of things to try, but it was the first thing that popped into my head. A bad ground could be leading to more waste heat on the normal circuit, increasing the rate of power loss a bit and could have a negative impact on charge rate when a higher amperage, or other hotter condition. If the small one to body, and the big one to alternator are good, I wouldn’t push it further.
 
Joined
Oct 17, 2019
Messages
34
Location
Washington
Did you blow the fuse in your multimeter?

This will vary by model but I have had meters that would pop after a few hundred mA.
I'll check it and see, but its a fair likelihood. I need to hook up one of the fancy ones that I use at work to see what the reading on there says.
 
Joined
Oct 17, 2019
Messages
34
Location
Washington
Could be a bad diode in the alternator.

OK so one thing I forgot to write up in the initial write up: I replaced the alternator with a Denso OEM rebuilt BEFORE the jump start fiasco. After that, I assumed the diode bridge in the alternator had failed so I went ahead and swapped it for yet another brand new OEM Denso unit so it has a literal brand new alternator in it right now and the issue remains. I think the wiring from the alternator to the battery could be the culprit so I think I am going to pull it again and inspect it more thoroughly this time. Other than that, I think my options include pulling the alternator and battery and taking them to autozone for testing.
 
Joined
Jan 2, 2003
Messages
5,355
Location
Georgia
No need to pull them unless the truck is in operable. Just drive in and they test in the parking lot. They also have a jump box if the truck won’t restart.
 
Joined
Apr 14, 2016
Messages
1,194
Location
Oregon
After that, I assumed the diode bridge in the alternator had failed so I went ahead and swapped it for yet another brand new OEM Denso unit so it has a literal brand new alternator in it right now and the issI think the wiring from the alternator to the battery could be the culprit
Just disconnect the big grey fusible link thick white wire in the fusible link cover and the multi-pin connector on the back of the alternator. Those are the only connections to the alternator. If the measured current drops, then you know it's the alternator (the diodes are built in to the regulator inside, in case you didn't know).
 
Last edited:

Irish Reiver

GOLD Star
Joined
Oct 24, 2015
Messages
1,879
Location
Orlando, Florida
@ElCheapo I think you need to circle back at look at what @jonheld mentioned a few posts back. If your draw was measured at 16.1 mA then you do not have a parasitic drain issue. To put that a different way, a 16mA draw on an 80A/h battery would, in theory, take 5000 hours to drain the battery - that's like 7 months. Now I know that in reality the truck wouldn't start long before the battery was drained but in any case you get my point.

Maybe time to restate your actual issue - how long does a fully charged battery last on your truck before it will not start the truck?
 

LandLocked93

SILVER Star
Joined
Jun 11, 2018
Messages
1,061
Location
Colorado
On the wire connecting the battery to the alternator, check the underside of the terminal connected to the alternator to ensure it is not making contact (or arcing) to the alternator case.
I experienced a draw there after not noticing the original terminal jacket/insulator/heatshrink had perished, exposing the terminal body to the alternator case. It wasn't physically touching the case. But it was close enough to cause low-intensity arcing between.
I found it by wiggling that wire and seeing sparks fly.
edit:clarity
 
Last edited:
Joined
Oct 17, 2019
Messages
34
Location
Washington
@ElCheapo I think you need to circle back at look at what @jonheld mentioned a few posts back. If your draw was measured at 16.1 mA then you do not have a parasitic drain issue. To put that a different way, a 16mA draw on an 80A/h battery would, in theory, take 5000 hours to drain the battery - that's like 7 months. Now I know that in reality the truck wouldn't start long before the battery was drained but in any case you get my point.

Maybe time to restate your actual issue - how long does a fully charged battery last on your truck before it will not start the truck?
So when the issue initially arose the battery would die within a few hours after letting the motor run for a while. I replaced the battery and it didn't get any better. I didnt have a multimeter at the time so I never got a chance to check for parasitic draw. I replaced the alternator and the issue seems better, but not fixed. It can sit for a few days before it goes flat now. Today I tore the alternator to battery harness apart again and I noticed that what @LandLocked93 said was somewhat true for mine, the heat shrink had fallen apart and the terminal crimp was very close to the alternator case so I re-heat shrinked it. I also noticed that the wiring on the connector for the back of the alternator had some missing shielding in it so I wrapped them in some aviation grade antichafe tape and then put a new wire shield over that. I did some resistance checks on the wires and found everything to be in good order so far. Will report back if I find anything else.
 
Joined
Oct 17, 2019
Messages
34
Location
Washington
If all previous suggestions fail, have you checked your grounds? It’s not high on the list of things to try, but it was the first thing that popped into my head. A bad ground could be leading to more waste heat on the normal circuit, increasing the rate of power loss a bit and could have a negative impact on charge rate when a higher amperage, or other hotter condition. If the small one to body, and the big one to alternator are good, I wouldn’t push it further.
That was actually one of the first things I did, Went through the engine bay and cleaned/preserved every ground point that I could find. I even did some of the ones inside the truck under the dash, to no avail.
 

Users who are viewing this thread

Top Bottom