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Unread 07-28-2014, 11:39 AM   #1
jrennard3
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12V Under the Hood Power Source

Hello!

Now, before you tell me to use Google or the search feature, let me explain something...I have no clue about the electrical components of my Jeep . All I know is that I need to run a wire to a 12v power source that is only transferring current when the key is in the ON position.

I've looked at my under the hood fuse box, considered other plugs under the hood, etc., but just can't wrap my head around what I should do.

Basically, I'm installing an external voltage regulator because the one on my main board stopped working. This device is cheap and supposed to work wonders, so I thought I'd give it a shot. Everything is hooked up and ready to go with the exception of the 12v source.

What is the safest and easiest way for me to take this little red wire and plug it where it needs to go? Thanks for your help in advance!! You guys have always been awesome and a huge help!

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Unread 07-28-2014, 11:52 AM   #2
NW99XJ
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The power distribution center ( or PDC for short) should have a switched (ignition controlled) circuit you could tap into.
So long as there isnt too much of a draw from the device you're installing,
you could piggy back off of one of the fuses that are already in there by using a fuse tap like one of these:




Otherwise you'll have to probe wires, and splice into one of the ignition controlled wires leading into the PDC.
I dont have a diagram in front of me, but if you have a test light, you can determine which circuit is hot with the key on.
(it would help if you had someone to run the key on/off duties while you're under the hood)
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Unread 07-28-2014, 11:54 AM   #3
jrennard3
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Very cool, where do you get one of those fuse taps? Is there a fuse in the PDC that would be better for something like this? The device doesn't require much from what I understand and won't draw a lot.
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Unread 07-28-2014, 11:54 AM   #4
wizardPC
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Quote:
Originally Posted by jrennard3 View Post
Basically, I'm installing an external voltage regulator because the one on my main board stopped working.
PUT. THE SCREWDRIVER. DOWN.

You have the technical ability to establish that a circuit inside your powertrain control module is faulty....but not the technical ability to identify a 12v switched source under the hood?

Step back. Take a breath.

Now. Explain to us exactly what is going on.

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Unread 07-28-2014, 11:56 AM   #5
jrennard3
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No, a professional told me that the PCM module was faulty. However, he wanted to have me spend $500 to replace the whole thing. I'd rather spend $60 to just fix the voltage regulator for the alternator.
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Unread 07-28-2014, 12:25 PM   #6
NW99XJ
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For some reason I thought all late model 4.0L's had internally regulated alternators.
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Unread 07-28-2014, 12:27 PM   #7
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Quote:
Originally Posted by jrennard3 View Post
Very cool, where do you get one of those fuse taps? Is there a fuse in the PDC that would be better for something like this? The device doesn't require much from what I understand and won't draw a lot.
But to answer your question, you can get them from any parts store.
As far as WHICH fuse.... IF you decide to go forward with this..... just use your test light to determine which of the circuits is hot when the ignition is on, pick one that 15amps or bigger, and NOT one that has anything to do with the ABS, or SRS/Airbag systems.
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Unread 07-28-2014, 01:43 PM   #8
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Quote:
Originally Posted by NW99XJ View Post
For some reason I thought all late model 4.0L's had internally regulated alternators.
No, they do not. The PCM (ECU) provides the regulation.

That said, it is VERY RARE for the PCM regulation function to croak and yet the rest of the PCM works fine. I would check EVERYTHING else before diving into the PCM.

That means check all grounds, all main power feeds, and especially the line from the PCM to the alternator that controls charging. If ANY of those are questionable, clean, refresh, and tighten all such connections first.
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Unread 07-28-2014, 02:00 PM   #9
wizardPC
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Yeah I don't think a regulator is going to fix your problem, for the reasons Jeff states. You can get a PCM from a junk yard for $75. I found one in Cicero. http:\\car-part.com is your best friend.

If your problem is inside the PCM, replacing the PCM will fix your problem. If it's elsewhere, then you'll have to take it back to the guy who gave you a frankly implausible scenario and explain to him that you tried to fix it via nonstandard methods. At that point, he might tell you that in addition to frying your PCM, you've also messed up your antigravity sensors and you need your blinker fluid topped off.

Or you can check your grounds first.
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Unread Yesterday, 05:05 PM   #10
jrennard3
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Thanks for the responses! We had the pro check all grounds, wires, and components battery and alternator related. All signs pointed back to the voltage regulator. They wanted to replace the whole PCM for $500. I'm still going to give this external regulator a shot, got some of those fuse taps and am just looking for a place to draw the power. I'll let you know soon!
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Unread Yesterday, 05:21 PM   #11
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Good luck!






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Unread Yesterday, 05:26 PM   #12
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Quote:
Originally Posted by wizardPC View Post
PUT. THE SCREWDRIVER. DOWN.

... but good advice ..


Quote:
Originally Posted by jrennard3 View Post
Thanks for the responses! We had the pro check all grounds, wires, and components battery and alternator related. All signs pointed back to the voltage regulator. They wanted to replace the whole PCM for $500. I'm still going to give this external regulator a shot, got some of those fuse taps and am just looking for a place to draw the power. I'll let you know soon!

In all honesty ... if it is the actual PCM causing the issue ... tis probably best to replace it with a new / refurbed or 2ndhand.

Charging rates are determined by the PCM according to a coupla inputs.

... what did the pro say about the temp sensor under the battery ... is it within specs .. ??
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