Alright this is gonna be a long one. I've been sifting through the forum for a week and now I think my brain is bleeding because I've got too much info.

I'm a novice, so be patient...

Rough driving on gravel roads, truck wouldn't start, wouldn't jump. Put a different battery in and it started, got me home (750 miles, never went more than 25-20hrs without being run). At home, sat for a day and a half, battery died.
**After I put in the different battery and the truck started, my buddy pulled the cables off the truck while it was running to "check the alternator" and I had a heart attack because I thought it may mess up the computer--maybe it did? Read on...**

Put in brand new battery and starter, ran that day, let her sit for 2 days and battery died. Rechecked wiring to starter, trimmed back some questionable insulation and cleaned things up, no difference.

Using a multimeter to test connections: when battery is weak (less than 11 ) and I hook up cables voltage RAPIDLY drops to about 5.5V. When battery is strong (over 11.8V) and I hook up cables, voltage RAPIDLY drops to about 10V then slowly drops from there. With a strong charge on battery it will drain in about 36hrs.

With either ONE battery cable hooked up there is no voltage drop, only when BOTH are hooked up.

Per the info I've gathered from this forum, I performed the following tests:

With the battery holding 10.5V, POS cable hooked up, multimeter between NEG cable and post set to read DC volts up to 20:

Pulled every fuse and relay (in cab and under hood), including EEC relay.
Reading dropped incrementally each time I pulled something (about 30 in total), but no single fuse or relay caused any significant drop; when I was done the meter read 10.8V.
When I hooked up both battery cables the voltage still rapidly dropped.

With the battery holding 10.8V and the multimeter in line with POS cable and post, I performed the same test but never had ANY change in voltage.

So I checked continuity across the top of each fuse. The 20amp maxi fuse associated with the fuel pump read .085. I replaced the fuel pump relay and the fuse: the fuse now reads no resistance but when I hook up both battery cables I still get rapid draw.

The EEC relay reads resistance of .085 when plugged in and I check for continuity across the terminals on top. What does that mean? I know enough to know that this may be misleading, but...

I checked the obvious grounds, all were tight and none showed significant corrosion.

Anybody out there who can help me out with this one? I would truly appreciate it.

Thanks,
Shep

 

Shep - I sort of got lost in the narrative, but bottom line, I believe, is that if the battery is connected to your truck, it loses its charge. Disconnect a cable and its all right - right?

So, something in your truck is putting a draw on the battery when everything is "off".

I'd suspect worn insulation somewhere (good luck here) in the positive wiring from the battery that is allowing a bit of leakage to ground. As I understand your narrative, you did not find any significant improvement in draw by pulling fuses.

I suppose, if you can let the truck sit for a long while, you could confirm this by pulling ALL the fuses and seeing what happens to the battery.

If it does not drop, start replacing them, one by one and see what happens. If you get a sudden drop, you've found the faulty component.

This problem is NOT an easy one to diagnose, in my opinion. I wish you luck!

- Jack

 

Jack-
Hey thanks for the quick response! And sorry about the narrative language; I kind of spilled it out in a hurry...

Yes, the bottom line is that I've got a significant draw on the battery and am having a very difficult time isolating it. The troubling thing is how rapidly the voltage drops when I hook up both battery cables.

I like your advice about pulling all the fuses...I assume this includes relays as well? I'll try this approach next, before beginning the tedious process of visually checking each wire.

Something I'd left out of my initial post: initially, disconnecting the voltage regulator stopped the draw, but today I replaced the regulator and the problem persists!

OK so I've replaced two components (regulator and fuel pump relay/associated fuse), both of which clearly suggested that they could be problematic (the voltage drop quitting when I disconnected the regulator, and the relay fuse showing resistance) but I still have a draw.

I agree. NOT easy to diagnose. I'll keep this post updated.

Thanks again,
shep

 

Shep - you're a man after my own heart!

Since those two components seemed to be culprits, have you gone over the wiring to them? And, is there any way to isolate these things off the system to see if the problem goes away?

The R&R appraoch DOES work at times, but not if the wiring's bad.

When I said fuses, I did mean the relays too.

What you really need to do is put an ammeter in the circuit. It should probably be one that can read up to 10 amps DC and you want to splice it in between the negative battery cable and the negative battery terminal. Hook the positive lead of the ammeter to the cable and the negative lead to the negative battery post. You shouldn't see much draw, as long as the interior and exterior lights are out and everything's off. I'd say anything above 0.05 amps is too much.

If you can disable the "door open" switch, so the truck thinks the doors are closed, with the ammeter connected, start pulling fuses. When you get a big drop in draw, you've found your problem circuit.

You can also look at this link, where a guy called wreedKR and I worked through this same problem: https://www.f150online.com/forums/en...-one-week.html

We have newer trucks, so some of our procedures probably don't apply to you, but the principle is the same.

Good luck, I'm going to be out of town (out of country) for the next three weeks, so I won't be able to offer more (possibly useless) suggestions. There's a guy called SSCULLY on this forum that may chime in though with some good ideas.

- Jack

 

Jack--
Well thank you. And you've given me a good amount of valuable information to work with. Good timing because I've gotten quite busy and, thankfully, have another vehicle to drive; it may take me a couple of weeks to work through this thing.

I haven't been able to do anything since my last post...kind of glad, because I was getting frustrated. Didn't know about using an ammeter, so hopefully using one will give me some info can use more effectively than the multimeter.

I'll definitely read the discussion you linked to me, and will look for SSCULLY if I turn up new data that confuses me again.

Have a great trip! Be safe, see you around the forum.

Shep