Parasitic drain

[df2x4]

Something else you could check is your underhood light. I discovered years back that the mercury switch in the underhood light of my red truck was extremely angle sensitive. If I parked on any kind of an uphill slope, it would stay on. I drained my battery by accident a few times before one night I happened to notice my passenger front wheel well was glowing...

 

[RawbDidIt]

For good measure, I checked the under hood light the glove box light and most other interior lights. They're on a different circuit, but hey, if it only takes a couple seconds, right? I'm leaning towards damaged harness with the increase in current when I checked there. What's likely to have happened is I pushed the lamp feed lead into the ground a bit further when I was checking, causing a spike in current. Easy enough to test, I'll pull the headlamp feed from the harness, should kill the drain immediately. If I'm right, should be a fairly easy fix, I'll just need to find a spare headlight switch harness, perhaps at a pick n pull and spend an hour soldering and heat shrinking. Worth every minute if the problem gets fixed. Could've found out yesterday, but the belt on my daily driver went out on the way home from work. Nearly cooked thre engine by the time I got home. By the time I got the belt replaced the sun was going down.

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[RawbDidIt]

And yes, a PO installed something earlier, not sure what exactly, there's 2 sets of wires, one goes all the way back to the rear near the splice made for the trailer lights, removed that, and another set that goes from the fuse block in the engine to under the dash. Both ends are disconnected from anything, I let that one be, I'll be using that wire to pull a feed wire into the cab for an amp once I get the electrical solid. I've been waiting to get this fixed so I can install a sub or two, but I'm not adding any more after market loads to the system until I'm sure the OEM electrical systems are all within spec. One variable at a time.

A PO also installed an aftermarket stereo, I pulled that a couple months back because it caused a short in fuse 14 circuit. That was a fun ride home at night with no dash lights... the guy didn't buy a harness, which isn't inherently bad, but he simply solder glued the leads together and wrapped it with a couple wraps of electrical tape. He clearly didn't plan on keeping the truck for very long, or he's never seen what electrical tape does after a couple years when it's not wrapped properly. Should've ripped it out when I saw the off brand Sears speakers he had in the front, but you live and you learn.

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[Schurkey]

Amperage can be measured anywhere in a simple circuit. Voltage must be measured near the intended load due to circuit resistance (or multiple loads). The amperage reading didn't change because you measured it somewhere else--unless the circuit branches, and there's multiple loads.

You have a "X" amp-hour battery. Let's say for the sake of conversation it's 100 amp-hours. This roughly correlates to a 600 CCA battery. A 300 mA drain would need 333 hours (Nearly two weeks) to deplete the battery. Several days, probably more than a week to drain it enough that it wouldn't crank the engine.

If the battery is being drained overnight (8--10 hours) either the battery is defective, it's under-charged to begin with, or the parasitic amperage load is much higher than 300 mA. Clearly, "less is better" with parasitic loads...but 300 mA doesn't seem like enough to present problems unless there's something else wrong, too.

Any chance this is a decimal error? Your meter showing 285 could be 285 mA, or 2.85 A.

 

[RawbDidIt]

Turns out all three of us are right (somehow). I agreed with you whole heartedly until it was draining a brand new battery overnight. And it's not a cheap battery either. Then I thought that it must be the problem because it's the only load on the battery with the ignition off. But that seems low for the symptoms right? Must be something else. Not necessarily, there is a third option. Turns out my readings were all correct. The harness connections for R and S were loose, so a slight jar would cause it to vary between 200 mA all the way up to 3.5 A. A slight jar caused by shutting the door, starting the engine, or general vehicle activity. This is why my readings were all over the place, and why what I thought was a low current could drain the battery overnight at times, or behave perfectly normally. I temporarily fixed it by placing epoxy on the harness to hold the wires in a position so they don't touch, and ordered the part. It'll be in later this week and I'll wire up the new harness.

So thanks, with the help of both of you, I was able to pinpoint the problem, and it only took me a week. Guess I'm not going to become a mechanic any time soon lol.

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[east302]

Glad you got it sorted out, thanks for updating.

 

[RawbDidIt]

I hate it when people post their problems and never the solution.

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