Jeep CJ-7 With Parasitic Electrical Current Draw

[Brian Lanier]

Greetings and thanks for the opportunity to share my story and hopefully get some insight on what's going on with my ol' trusty Jeep.   I have an '83 CJ-7 with a parasitic draw that I have been unable to isolate.  This problem has presented only recently.  I have inspected it in pitch dark and have found no lights burning, either on the outside or interior/dash.  It has a new battery.  I have attempted to use a digital voltmeter to assess the current being drawn but I get variable readings (sometimes zero) despite the fact that I always see a little spark when I reconnect the knife-type battery cutoff.  When I did measure a current, I have pulled each blade-type fuse individually from the fuse box without any drop in the reading.  There are no "extra" devices currently wired outside of the fuse box like lights or radios.  Leaving the battery connected results in a completely depleted battery in just a few hours.  Since this problem started, I've had a couple of times that the engine wouldn't shut off.  I replaced the ignition switch with a new Duralast unit which works as expected, but I still have the parasitic draw.

 

My question is, could anyone provide a logical progression of diagnostic steps beyond what I've done already?

[Moses Ludel]

Hi, Brian, and Happy New Year 2021!  You've been thorough in your approach.  To begin troubleshooting based on your facts and findings, there are two things I would immediately check:  1) see whether the fender mounted solenoid switch is defective, this is an inexpensive item that can feed current both ways or bleed voltage and 2) check the alternator for a bad diode or current bleed-off/draw when the key is off.  Simply disconnecting the main lead to each of these devices (one at a time) and doing your knife cutoff check should be telling.

Gauges can sometimes cause these issues, but that usually requires KEY ON, so I'd somewhat rule this out.  As a routine step, confirm that all grounds are working and not creating resistance.  The engine and alternator need a direct ground from battery.  Engine to body and engine to frame grounds are essential, too.  Another focus would be the light switch or dimmer switch, which each work independently of KEY ON.  Either can draw current without the key in the ON position.

Finally, I'd look for devices that have a direct battery lead like the ignition module or the ECU/microprocessor.  The carbureted CJ models do have a feedback O2 sensor system and microprocessor.  Disconnect each off of these devices independently and do your simple knife cut-off check. 

If you have a winch, disconnect the battery lead to the winch and perform the knife blade cut-off check.  There could be a parasitic voltage draw at the winch controller, its solenoid (some, like Warn, use a solenoid similar to your starter solenoid) or even conductive dirt or mud across the contacts that can leak to ground. 

I'd target the starter solenoid switch first, especially with the engine run-on before and after your ignition switch change.  The run-on after KEY OFF is a trouble symptom with this traditional AMC or Ford (Motorcraft) type solenoid.  Run-on and parasitic draw can also occur when the starter motor drive and solenoid switch stick;  however, this is a direct short with high amperage that will toast the battery cable. 

Trust this helps.  Let us know if it does, and if not, we'll take the troubleshooting to the next step.  When troubleshooting like this, I perform one step at a time to isolate the specific problem.  You want to know the actual cure and not just replace a batch of parts.

Moses

 

[Brian Lanier]

Hi Moses, thank you for your thorough recommendations.  I forgot to mention in my original post that I as started the process of replacing the ignition switch (Duralast PN LS442), my starter failed and I replaced it with a remanufactured model as well as the solenoid with Duralast PN AM431, so this is a brand new unit.

Today I think I have realized that I exceeded the 10A limit on my digital multimeter which is why I am no longer reading any current.  However, when I complete the circuit at the knife cutoff with a 12-volt test light, the light shines BRIGHTLY.

I have gone through the following steps in this order per your recommendations:

- disconnected and reconnected the alternator.

- disconnected and reconnected the ignition module

- disconnected and reconnected the headlight/dimmer switch.

- disconnected and reconnected the ECM/ECU.

With all of these steps, the test light continues to shine brightly.  I’m not sure what the feedback O2 sensor and microprocessor look like, but I have disconnected every harness I can find under the hood with the same results.  The Jeep does not have a winch, and I have done my best to ensure that no other accessories are connected.

UPDATE: My suspicion of a higher current draw led me to purchase a higher amperage AC/DC clamp meter.  The current at the main positive battery terminal was almost 12A!  In tracing out the current I was led to a relay that was notably warm.  As I continued to troubleshoot, the current dropped to a negligible level and I noticed that the relay began to cool.  I suspect that this relay is part of the problem but it would have been more satisfying if the current had dropped after I removed it rather than spontaneously.  The relay is deformed on one side and there is evidence of heat damage to the connector adjacent to the largest gauge wire.  With the relay removed the Jeep cranks and runs, and a cursory inspection reveals nothing that is no longer functioning (lights, gauges, etc).  This leads me to the following questions:

- What is the purpose of this relay?  

- Is it possible/likely that the relay itself is the source of the draw, or whatever it supplies power to?

[Moses Ludel]

Hi, Brian...The black contacts on the relay are a hint that continuity is poor.  An electrical contact spray cleaner (do not scrape contacts) will help get rid of the black oxidation in the socket. 

It's likely that this relay has an internal short and is bleeding off voltage to ground.  If at a lower amperage rate draw, the fuse may not blow.  Check voltage and ground resistance at the terminal poles of the relay socket.  Considering the parasitic loss, see whether the hot terminal is live at all times and not just when the key is on.  This feed could be to the headlight switch or other higher amperage circuits, as the ceiling on the relay is 20/30 Amps.

Determine which device(s) the relay drives.  Check that device for normal function.  If it's the headlamp switch, make sure the vehicle's body-frame-engine and lamp grounds are good.  12V-D.C. requires the same ground load capacity as the hot lead(s).  You can quickly check chassis and body ground circuit resistance with a volt-ohmmeter.  Place one probe at the battery negative post and the other to a bare frame or body point.  Read ohms resistance, not just the continuity.

Of course, this could narrow down to simply a defective relay.  You can test a relay, but from your description and the photos, this one is done, anyway, and should be replaced.  Relays have a duty cycle and wear out, especially this Bosch type.  If the relay is for the headlight circuit, test and make sure that the headlight and dimmer switches are not defective and bleeding voltage to ground.

Again, check the relay socket terminals, verify whether this circuit is live voltage with the KEY OFF.  Determine what device(s) work from this relay.  Troubleshoot as necessary...Let us know how this turns out.

Moses