Mystery battery drain 2018 Ram 3500 pickup/Cummins 6.7/Aisin

[DonRam240]

At first this seemed to be a bed light that would turn on spontaneously, and we disconnected the LED circuit connections at the light curing that part. But the dying battery problem either continued or resumed (thought cured for a few weeks but don’t know if “tested” so am unsure of that). Normally since new, if truck is parked for more than several days I keep it on maintenance charging, but a few days is too long now.
Seems about 2-3 days not on maintenance charger to very dead batteries (5v on measurement before charging). No lights “on” are involved this time. Fortunately now have AGM batteries that will recharge well after this abuse. No trouble codes so far, and there were none when bed light was active either.
What are the likely possibilities? Thanks for your anticipated help!

 

[petersonj]

My first step would be to fully charge the batteries and then disconnect the ground at each battery. Let them set for a day or two and then recheck battery voltage. I would do this test regardless of how new the batteries are.

They will either pass or fail the test. Either way, you will know what direction to proceed.

- John

 

[lpennock]

Could be a bad battery. Have you tried disconnecting them and see if one has low voltage after a couple days?

 

[Ozymandias]

An LED bed light doesn't have the capacity to drain a battery dead within a reasonable time.

 

[Grumpy8811]

assuming your batteries pass a load test, you could put an ammeter in series with battery , set on milliamps and see what the parasitic drain is...
if it has a hi draw start pulling fuses and relays until you figure out what the culprit is and proceed in that direction
.

 

[Topzide]

If you have a connection unplugged, could be tracking across that connection causing part of the drain. Tracking can cause you to loose your mind! Hard to see/find, but big headaches! Charging them up and disconnecting them would be my first go to. If no drop, the hunting begins! Good luck on the hunt.

 

[Diesel85]

I was looking for something else on Amazon and came across this...

https://a.co/d/aHb0UIK

Now I'm interested in getting one for my truck just for the data.

 

[Topzide]

@Diesel85, Pretty neat looking device, not sure that I want to add another device to drain a system that seems to have enough drains on it! I also don't like that it will broadcast a Bluetooth signal all the time. Some phones limit the Bluetooth signals that it connects to, and this could cause conflict with other devices that are more important to connect with. I have a voltage display that is wired in to be on with ignition. Thinking about getting another to wire to left and right batteries, instead of just a combination of the two. Just my thoughts on it. It would be better suited for me to be on my tractors.

 

[Hoefler]

How old are the batteries?? Have them load tested first! Before any other attempt of diagnosis.

 

[DonRam240]

Thanks for the responses. After systematically excluding other drains at TIPM with a sensitive DC ammeter, we noticed that two of the five “upfitter” switch circuits had somehow been jumpered so they were “B+”, on with key off. Don’t ask me how I hadn’t noticed this before, just wasn’t informed by either of the folks who accessed those circuits that they did this. One was drawing 3 amps to a camper battery charging relay. With that fixed by moving both of them to “IGN+” circuits the battery draw is only 40 ma. We should be good now, will watch voltage off charger a few days to confirm.

 

[AH64ID]

Thanks for the responses. After systematically excluding other drains at TIPM with a sensitive DC ammeter, we noticed that two of the five “upfitter” switch circuits had somehow been jumpered so they were “B+”, on with key off. Don’t ask me how I hadn’t noticed this before, just wasn’t informed by either of the folks who accessed those circuits that they did this. One was drawing 3 amps to a camper battery charging relay. With that fixed by moving both of them to “IGN+” circuits the battery draw is only 40 ma. We should be good now, will watch voltage off charger a few days to confirm.

Are you referring to physical “jumper” or programming of the Aux switches?

 

[DonRam240]

Are you referring to physical “jumper” or programming of the Aux switches?

The “jumper” refers to Aux switch programming. Have not done this myself, just using term from upfitter info sheet. I’m assuming someone did it for switches 1 & 2 because I don’t know another way they could have become B+.
If I need one of them in future will have to follow directions to make them I+.

 

[AH64ID]

I believe Aux 1 and Aux 2 are factory programmed to B+.

Jumper isn’t the correct term for programming, it is listed in the upfitter sheets, but deals with physical jumpers to the wiring harness.

 

[DonRam240]

I believe Aux 1 and Aux 2 are factory programmed to B+.

Jumper isn’t the correct term for programming, it is listed in the upfitter sheets, but deals with physical jumpers to the wiring harness.

Thanks for the information, will add to my Upfitter file for reference.
Don