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Discussion Starter · #1 ·
I took my batteries out. Put them back in. Driver side, I knew what I thought was -/+ but I guess when I swung the damn thing back in place, I crossed the cables. Took it off instantly when it started sparking. Truck is fine… now I have a drain. 6 days later and the battery is dead. I took the terminals off b/c it will drain and ruin the batteries.

The only things I know that can drain are closed relays/solenoids. Fuses not so much.

I’m thinking this might cost me a new engine harness. Will be checking every relay next weekend.

Anyone have experience in these situations / shenanigans and what tools to find the drain? I’m a dummy, I know. Thanks in advance.


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Typically it's measure voltage, take one fuse out, check voltage tomorrow, repeat till found.
 
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Discussion Starter · #5 ·
Typically it's measure voltage, take one fuse out, check voltage tomorrow, repeat till found.
I believe the fuses has nothing to do with it b/c it’s always on. However, what ever connecting to it before the fuse such as a relay, can he the culprit.

Measuring the voltage will only tell me the overall voltage but not the draw. I tried using my amp reader but that’s only for ac.

My first thought was measuring draw but I don’t have one - maybe it’s times like this giving way for more tools.

Reason I ask is on the 6.0 - there’s a lot of electronics connecting to a lot of other systems. If this was a gas motor it would be easier for me.


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Discussion Starter · #6 ·
Unplug your alternator and see if that stops the draining.
I’ll give this a go tomorrow night after I get off work. The batter is on the charger right now.


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The reason you pull the fuses is to isolate the circuit that is causing the draw. When you pull the offending fuse, the draw will lessen. (There will be slight draw just because of electronics) Anything over .05 is a problem. Then you troubleshoot that circuit to find the draw. Remember you have 2 batteries, you need to disconnect both negative cables and troubleshoot from the negative terminal of either battery.
 

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Checking one fuse a day would work, but it would be AGONIZINGLY slow. And it wouldn't test any of the unfused circuits. Measuring voltage is not very effective until the batteries are nearly dead.

The correct way to test is to install an inline current (Amp) meter between the only battery (leave the other disconnected) and its negative terminal. The parasitic draw should be (by industry standard) <50mA (0.050A), but is typically in the 20mA range. Remember that some circuits/modules "wake up" when power is applied, including turning the key to RUN or when the first battery is re-connected. So they can draw substantially more until they go to "sleep", which can take ~30 min for some.

If you find the parasitic draw is in-spec after all the modules go to sleep, the truck is not killing the batteries - at least one of the batteries is killing itself, which is killing the other (because they're in simple parallel). Leaving one disconnected from the other should quickly ID the bad battery because its voltage will drop rapidly &/or it won't take a charge.

But if the draw is significantly higher than spec, start pulling fuses while watching the meter. When it drops, you've either disconnected the power to the draw, or the power to the module or switch that's keeping the draw turned on. Remember that some fuses are elsewhere, and some loads are not fused, so you may not find it from the underhood fuse block.

But ANYTHING that can kill 2 diesel cranking batteries in a day should be NOTICEABLY HOT after a few minutes of being connected to 2 charged batteries, so that's another way to find the problem. Hot like the glow plugs, because that's about how much current it would take to kill the batteries that fast. Even if it's one of the batteries, they'll both get warm. (The heavier the object draining the power, the cooler it will be.)
 
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If you don’t have a dc amp meter you should be able to find your problem with a test light.
Connect the light from negative cable to negative battery post, the light should glow fairly bright (depending on draw) when you remove the fuse to circuit drawing power the light will dim. If it never changes then you remove fusible links one at a time. If you have to pull fuses from the panel inside cab be sure to disable door switch to courtesy lights. I’m still thinking that reversing battery polarity probably took out your voltage regulator and when you unplug the alternator it will stop draw. You may even be able to feel casing for heat.
 

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That only works with an incandescent 12V test light - not LED. And the bigger the bulb, the more-sensitive its brightness will be to the current draw.

The VR isn't really affected by reverse polarity - it's the rectifier (diodes) that will usually explode. And not just in the alternator - this is in a gasser EEC:

This diode blew just from age & load - not polarity.
 
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Discussion Starter · #11 ·
Just picked up a 1mA dc amp reader. Will keep you all posted. Great advice above.


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Just picked up a 1mA dc amp reader
That would be NASA-level to read such a small current. 5~10A is a more-common range for inexpensive meters. Most don't go above 15A unless they have a large inductive clamp.
 

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Discussion Starter · #13 ·
That would be NASA-level to read such a small current. 5~10A is a more-common range for inexpensive meters. Most don't go above 15A unless they have a large inductive clamp.
I already have one at home that I use but it won’t read higher than am amp. I also tried to use it and it didn’t work so I’m hoping this one works.




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1ma is the meters sensitivity. That meter should work for you. The meter you have that isn’t working, did you check the fuse, it’s easy to blow one without realizing.
 

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Discussion Starter · #16 ·
1ma is the meters sensitivity. That meter should work for you. The meter you have that isn’t working, did you check the fuse, it’s easy to blow one without realizing.
No it’s not, it’s specifically tailored towards hvac. Yeah I’ve blown a few fuses On the RadioShack units but this one’s been great.


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