For all electrical troubleshooting... [Archive] - JKowners.com : Jeep Wrangler JK Forum

: For all electrical troubleshooting...


StubEXrube
09-15-2008, 05:10 PM
Since there are quite a few different elec problems that people are asking about...I wanted to confirm what is the safest way to go about disconnecting the battery to either diagnose or perform work on the JK.

Should you disconnect only negative?... only positive?... or both?

Should the ECU also be disconnected anytime you disconnect the battery?...or only when doing certain procedures?

The ECU is located where on drivers side?...(The two huge connectors on the firewall?...or the three smaller connectors on the washer fluid reservoir?)

How long should the battery be disconnected for, in order to "reset" the computer?...Several minutes? Overnight?

* Thanks to anyone that can answer these questions.

ColinW
09-15-2008, 05:51 PM
Should you disconnect only negative?... only positive?... or both?

Negative first, always...it will prevent arcing that may occur if you disconnect only the positive. Disconnecting only the negative will suffice...just make sure you secure it away from the negative post and away from metal. If you want to, you could do both terminals to be sure the system doesn't get powered up by accident.


Should the ECU also be disconnected anytime you disconnect the battery?...or only when doing certain procedures?

You don't need to connect the ECU unless you are hooking up another power source...doing the battery is sufficient.


The ECU is located where on drivers side?...(The two huge connectors on the firewall?...or the three smaller connectors on the washer fluid reservoir?)

Near the three connector deal - in that metal plate looking thing, I believe.


How long should the battery be disconnected for, in order to "reset" the computer?...Several minutes? Overnight?

Not sure exactly how long, but I've had my battery disconnected for about 5 mins before and everything seemed to reset, as the tell-tale horn honk went off when I reconnected the battery.

dyolfknip
09-15-2008, 07:22 PM
Negative first, always...it will prevent arcing that may occur if you disconnect only the positive. Disconnecting only the negative will suffice...just make sure you secure it away from the negative post and away from metal. If you want to, you could do both terminals to be sure the system doesn't get powered up by accident.




Sorry man, I have to disagree.
If you leave a hot side on you leave WAY too many possibilities for something to act as a ground. If you have the red on you still can get arcing, and depending on your battery it will be quite a distance. I am an electronics tech and from day one when being taught to use a DMM you are taught to connect to ground first, then positive, that way you arent prodding around with a hot lead.


To the OP....whenever I work on something electrical I pull the positive and slide something non conductive (old rubber antistatic mat) under the red cable and on top of the battery terminal. Honestly if you are really leary just disconnect both. I so dont want to be the guy who is responsible for you becoming the ground for 1000 cold cranking amps....:shaking:

dyolfknip
09-15-2008, 07:24 PM
Not sure exactly how long, but I've had my battery disconnected for about 5 mins before and everything seemed to reset, as the tell-tale horn honk went off when I reconnected the battery.

Also from what I have read on "other" forums you can touch the two batt wires together (obviously disconnected from the battery and it will "reset"...havent had the need to try it out yet though.

John L
09-16-2008, 07:05 AM
Also from what I have read on "other" forums you can touch the two batt wires together (obviously disconnected from the battery and it will "reset"...havent had the need to try it out yet though.

Yeah, I read that too. Bleeds off anything left in a cap.

Alec W
09-16-2008, 01:23 PM
I only tend to disconnect the positive side and put a rag between the cable and the terminal. Iíve read that some folks disconnect the ECU when they are welding directly to the rig but I havenít done that and nothing has fried yet.

If in doubt disconnect both terminals and the ECU, itís not like it takes very long.

ColinW
09-16-2008, 05:51 PM
Sorry man, I have to disagree.
If you leave a hot side on you leave WAY too many possibilities for something to act as a ground. If you have the red on you still can get arcing, and depending on your battery it will be quite a distance.

Yeah, I suggested making sure you secure the negative away from all metal which can work if you pay attention, but that is probably a better route.

I am an electronics tech and from day one when being taught to use a DMM you are taught to connect to ground first, then positive, that way you arent prodding around with a hot lead.

That's news to me...you always remove the positive first? I always remove the negative first and connect it last...same kind of thing when you're hooking up batteries in parallel when jump starting a car - you want to connect the negative to the dead battery's engine block last to prevent arcing and explosion from the spark and hydrogen around the battery that could occur if you connect the positive to a battery last, and remove it first.

I can see why you would want to do that on a circuit away from the battery - so you have a certain ground before completing the circuit; so you don't become the ground, but I would think that when you're working around the battery, you may want to do the opposite for a little more safety?

dyolfknip
09-16-2008, 06:38 PM
Yeah, I suggested making sure you secure the negative away from all metal which can work if you pay attention, but that is probably a better route.



That's news to me...you always remove the positive first? I always remove the negative first and connect it last...same kind of thing when you're hooking up batteries in parallel when jump starting a car - you want to connect the negative to the dead battery's engine block last to prevent arcing and explosion from the spark and hydrogen around the battery that could occur if you connect the positive to a battery last, and remove it first.

I can see why you would want to do that on a circuit away from the battery - so you have a certain ground before completing the circuit; so you don't become the ground, but I would think that when you're working around the battery, you may want to do the opposite for a little more safety?


Ya after I posted last night I did a little research and even when jumping batts they say do the pos first.....weird...oh well havent electrocuted myself yet lol....:beer:

StubEXrube
09-16-2008, 08:31 PM
This thread deserves a couple of stars, imo. You guys have all been a great deal of help...and maybe saved me from potential death. I'm sure that this info will help out others as well. Thanks very much!