Mystery Problem - What is draining my battery?

Hi all,

I have a 1995 Bronco 5.0L with a mysterious battery drain of about 200ma. I have used a clamp-on ammeter on the negative cable to the body as well as an inline ammeter between the terminal and post. I mostly use the clamp-on because it is easier but the values fluctuate between 170 - 300ma. The battery voltage was 12.33v two days ago. It is 12.22v today.

- Checked the alternator to see if diodes were leaking. It tested good. No change.

- Checked each fuse inside and under hood with a voltmeter to see millivolts. There were three possibilities and each fuse was pulled ( and yes, I closed the door to turn off the dome light).  No change.

- Pulled each fuse, circuit breaker, flasher, diodes, and relays one at a time. No change.

- Pulled ALL fuses, circuit breaker, flasher, diodes, and relays inside and under hood. No change.

- Replaced ignition switch under steering column. No change.

- Replaced key cylinder for another issue. No change.

- Unplugged airbag control module under dash. No change.

- Unplugged PCM from engine compartment. No change.

- Removed starter relay from side wall (no ground means no circuit). No change.

- Removed alternator again. No change.

- Removed battery. NO DRAIN.  haha  Just kidding.

I am stumped! The dent is getting bigger from beating my head. What else could be leaking with the key off?

Thanks,

Tom

... continued

The positive cable from the battery splits and connects to the starter motor and the starter relay. There are four or five smaller wires also on the starter relay. I am thinking about removing one wire at a time. I know this is fishing but I am out of ideas.

Hmmm, I did not disconnect the starter motor or solenoid underneath.

Check wires that run through or near metal.  Over the years vibration can cause a rub through that isn't a dead short but causes a small current drain.  It sounds like you have done a pretty good job of trying to isolate the circuit that is drawing current but you must have missed something.  I'd go back through it again starting with major branches including those wires on the start relay.

Good luck,

>-

Yo tom,

As seabronc advised and...

http://broncozone.com/topic/22079-battery-drain-when-off/

Significant info:

Diodes inside the alt could be leaky/shorted, thus causing drain, but the it could still put out between 13.0 & 15.0 volts w/engine idling & pass the Voltage Output Test, however it could not put out full current, & would fail the Current Load Test.

Remove & Charge Battery and take voltage reading (should be around 12.6 volts)

Disconnect alternator, then re-install battery for a day or so & then check batty voltage again; if no drain, then diodses are prob the issue.

do you have an under-hood lamp? if so, disconnect it, but be careful of assy since it is prob contains mercury

Under-Hood, Mercury Removal Guide, Bronco, Ford, 70-95, etc. Source: by wa.gov/pubs

Notice that they left out our Broncos in the Listing.. but incl BII & F-Series Truck (F 150-550) 1974-2000

See 96 bronco workshop manual partial

http://www.diesel-dave.com/vehic/manual/stj/stje0007.htmSame as most earlier years especially 92-96, excepts for OBD II in 96, 4WABS (93-96); ABS (87-92); Air Bag (94-96); 3 ***** Automatic Locking Hubs (Built from May 95 through 96); Spark Plug Wire Routing & Firing Order (The firing order for 1987-1993 5.0Ls is 1-5-4-2-6-3-7-8. The firing order for 1994- 96 5.0Ls & all 5.8Ls is 1-3-7-2-6-5-4-8.);

2-piece Spindle Rolling Diaphragm Seal (RDS) used on 5/95 to 96 Broncos & F Series 1/2-ton 4WD

and a few other items that I still need to research

14-00: Battery and Charging System, Service

1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual

DIAGNOSIS AND TESTING

Component Tests

http://www.diesel-dave.com/vehic/manual/stj/stje0007.htm#extract_1397

Thanks Seabronc and Miesk5. The alternator was tested multiple times at Autozone and passed. Also, I took the alternator off and the drain was still present. There is no hood lamp. I will charge the battery and then check everything again as well as look for wires against metal.

Thanks,

Tom

Here is an update:

I started from scratch. Turns out that using a meter on the negative cable is unreliable. The clamp-on meter was showing 140ma (after zeroing) with the positive terminal removed from the battery which is impossible. I used my trusty regular ammeter inline with the positive terminal and this showed a constant 120ma (0.12a). I was ready to chuck the clamp-on meter but tried it one more time on the positive cable and this also showed 120ma (0.12a). I went through all fuses again starting under the hood and I found **** fuse #9 or letter "i" is the draw. Also, a voltmeter across this fuse showed 3 micro volts while all other fuses showed 0 which is expected when nothing is running. I pulled this fuse and the draw went down to 10ma (0.01a). Fuse #9 says PCM power relay and the PCM itself (pin #1). I pulled the relay and no change. So now I have the Haynes manual with wiring diagrams looking at each thing the PCM connects to. Many connections are for the E40D transmission as well as various sensors and solenoids. This could take a while.

Thanks

Yo g,

This is for free & on-line @ http://www.revbase.com/BBBMOTOR/Wd

Wiring diagrams & Technical Service Bulletins (TSBs) are same as by Ford in Powertrain Control/Emissions Diagnosis (PCED/EVTM) Manuals

Power Distribution Box

Diagram in a 95

Source: by Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums

http://broncozone.com/topic/21047-1995-bronco-fuserelay-question/?s=3da518f17e564315aa74c5401c99f946

This info conforms to what you have in Haynes so far.

See my archived "short circuit" section at

http://web.archive.org/web/20101224103239/http://www.broncolinks.com/index.php?index=1058.

One May apply

And..

Short Circuits, Common Locations TSB 95-02-11 on 94-95 Bronco & Trucks; See O. Fuse 13 Blown

Source: by Ford via Steve

http://web.archive.org/web/20070529142854/http://www.supermotors.net/vehicles/registry/media/470456_1

GreenMachine, I just had to replace the alt. on my 90EB, (battery running down).Same problem with the new alt. So i started looking and found that a "fuseable link", green wire connected to the solenoid was burnt inside the insulation. I noticed when I pulled on it and saw it stretch. I cut it out and put a new connector, works great now. not sure if something similar could be your issue, but thought i would share.

Bronco90EB said:

GreenMachine, I just had to replace the alt. on my 90EB, (battery running down).Same problem with the new alt. So i started looking and found that a "fuseable link", green wire connected to the solenoid was burnt inside the insulation. I noticed when I pulled on it and saw it stretch. I cut it out and put a new connector, works great now. not sure if something similar could be your issue, but thought i would share.

Click to expand...

You should replace a fuse link with another one or a fuse of equal current rating to protect your alternator from a system short.

>-

Excellent info. Many thanks. I will be looking through the TSBs and wiring diagrams along with my Haynes manual. Note that there are no blown fuses so I don't think there is a short circuit. Thanks again.

GreenMachine said:

Excellent info. Many thanks. I will be looking through the TSBs and wiring diagrams along with my Haynes manual. Note that there are no blown fuses so I don't think there is a short circuit. Thanks again.

Click to expand...

No, they seem to go bad over the years, but that is what they are for.  They serve the same function as an under the hood fuse box on newer vehicles.  A couple of the fusible links shown in the wiring diagram are buried the wire harness.

Good luck with your truck,

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