Electrical headscratcher!

[Trio3b]

1997 Ford E350 Clubwagon. Vehicle used only 3-4 times per month

Symptom: battery dead about 1 month ago. Discovered dome light on. Recharged and fine until last week dead again. This time triple checked all interior lights and controls set to off. Recharged battery - dead next day.

What's been done:
1. Inserted test lamp between disconnected neg cable and battery neg. Lamp lights.
Reconnect neg and Inserted test lamp between disconnected pos cable and battery pos. Lamp lights both ways indicating parasitic drain

2. Pulled fuses starting in engine compartment. Lamp goes out when pull fuse that feeds INTERIOR fuse panel. Reinsert fuse.

3. Ok.Move to interior fuse panel and pull all interior fuses one by one reinserting as I go. Lamp stays on the whole time. Recheck this 3 times.
4. Eventually took to mechanic. Turns out to be battery according to him. So far so good. That was 3 weeks ago. I asked him specifically what caused the drain. He said battery.

Question: The fuse pull method this has got me through 50 years of diagnosing electrical drains.
Call me cynical but I think mechanic found something simple I missed was draining battery and he used opportunity to sell me a new battery. What say you?

[Stealthee]

Originally Posted by Trio3b

1997 Ford E350 Clubwagon. Vehicle used only 3-4 times per month

Symptom: battery dead about 1 month ago. Discovered dome light on. Recharged and fine until last week dead again. This time triple checked all interior lights and controls set to off. Recharged battery - dead next day.

What's been done:
1. Inserted test lamp between disconnected neg cable and battery neg. Lamp lights.
Reconnect neg and Inserted test lamp between disconnected pos cable and battery pos. Lamp lights both ways indicating parasitic drain

2. Pulled fuses starting in engine compartment. Lamp goes out when pull fuse that feeds INTERIOR fuse panel. Reinsert fuse.

3. Ok.Move to interior fuse panel and pull all interior fuses one by one reinserting as I go. Lamp stays on the whole time. Recheck this 3 times.
4. Eventually took to mechanic. Turns out to be battery according to him. So far so good. That was 3 weeks ago. I asked him specifically what caused the drain. He said battery.

Question: The fuse pull method this has got me through 50 years of diagnosing electrical drains.
Call me cynical but I think mechanic found something simple I missed was draining battery and he used opportunity to sell me a new battery. What say you?

I agree with your assertion. Something small was overlooked and he took advantage of it.

[shorod]

Help me understand the timeline. You mention the battery was dead a month ago, then say it died again last week, you did some tests, took it to a shop where the battery was replaced, and it's been good now for 3 weeks. So ultimately has it been 3 weeks since the battery was replaced and no further instance of an issue? If so, I wouldn't be totally convinced something was overlooked. Do you know how much current is required to light your test light? It's possible the PCM, radio, body control module, etc. were drawing just enough current, including possibly standby current from recently opening the door, to keep the test light lit. Now if you pulled all fuses from the interior at the same time and the light still stayed on, that would be confusing.


-Rod

[Trio3b]

Initial battery drain was due to leaving dome light on. But when it happened a month later and subsequent charging and still dying several times, I suspected a drain bc I made sure everything was off. That's when pulled fuses one by one but it never produced a clue. Not sure of current required to light the lamp.

Kinda disappointing about the mechanic bc I been with him close to 40 yrs now and I consider his work to be really good (and I've tried many over the years). Lately though he's been sending out personal texts to myself and someone else I know soliciting work which he's never done before. That seems weird.

He knows I do 90% of my own wrenching but use him when I'm jammed for time or stumped. Maybe he figures if he tells me what the real problem was then he's giving me ammo to diagnose similar problems down the road and therefore less business for him.

Hate to think that way but makes sense. In his defense I know that Ford did have a body control module called the g e m that is supposed to detect inadvertent interior lights left on but can actually cause drain itself when it goes bad and is a real PITA to diagnose. But if the PCM or the body module was bad, he would have charged me for it . Trust me . And he didn't ....so my conclusion is that I missed something simple and he used the opportunity to clip me for a new battery, Dang it. Either way, it's been several weeks now and Battery seems to be fine.

Anyway, thanks for the help. Gonna have to let this one go.

[brcidd]

I have never used the test light method for amp draw--I always put my DVM on current draw (DC amps) setting and use it in series like you do the test light- Then I have a real number and can watch the PCM BCM go to sleep. A .050 amp draw is considered the max allowable. Thats 50 milliamp- so your battery should stay "up" with 50 milliamp or less draw...use your DVM to its fullest ability...and you won't have to wonder how much current it takes o light your test light.. (you could discover the amount by using your DVM-BTW)

[Carfan32]

What does it mean to run something in series

[shorod]

Originally Posted by Carfan32

What does it mean to run something in series

When it comes to connecting things in an electrical circuit, they will either be connected in series or in parallel. A very common item to be connected in series within a car is a fuse. Think of this series connection as essentially cutting the power wire and placing a fuse "in series" across the two ends of the cut wire. All current in the circuit must flow through that fuse in series with the circuit.

That series fuse will often feed multiple items connected in parallel. Items connected in parallel will be all be connected to the same feed and the same ground. So the series fuse and associated wiring needs to be rated sufficiently to be able to supply current to all of the parallel devices on that circuit.

A water flow analogy is often used to help visualize electrical circuits and current flow. If you think about a garden hose spigot with a three-hose tap connected to it, the spigot on the outside of the house is like the fuse mentioned above, and the three garden hoses would be like devices connected in parallel to the fused circuit.

I'm sure there are better ways to describe it if this is still confusing, but my lunch break is about over.

-Rod

[brcidd]

Probably the best and most informative site I've ever used for the last 20 years or so is www.the12volt.com.

https://www.the12volt.com/

It has numerous diagrams of the most simplest circuits and very good explanations of how to wire and test- on anything car electrical.

I used it extensively when I installed remote starters and built relay timers etc
It goes back to the basic things like resistors and capacitors and Ohms Law stuff.

I recommend it to anyone who wishes to do automotive diagnosis.

[tomj76]

The test light method works well, even today, but it is a coarse measurement. A meter (analog or digital) can be much better since it reports a number.

I believe there is a third option. Your mechanic might have fixed the problem. Once your old battery had been fully depleted it was chemically damaged and it's capacity was certainly compromised. This would make it sensitive to a parasitic drain.

I've seen some strange battery behaviour over the years. For example, I once had a battery that would start the car fine, but AFTER driving the car for 10 miles or so it couldn't start the car again. If you let the car sit for many hours it would start fine. I tried charging it over night, I tried a about 100 things, and eventually realized that the battery had an internal problem that was causing the internal resistance to rise with temperature.

The point is that you could have just simply needed a new battery.

The other fact to consider is that the electronic circuits in vehicles will often draw a significant current when they are first powered up, then after some time go into a low power state of "sleep". When my son's car had a drain, we were doing just as you did, pulling fuses to find the circuit causing the drain. However, this testing was complicated by the fact that some circuits didn't drop down into their low power state until they had been operating for time periods of any where from 30 sec to 3 minutes. If you didn't wait long enough when doing the fuse pulling tests, you might not have seen the true amount of parasitic drain.