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2002 chevy trailblazer_ls
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Discussion Starter · #1 ·
None of my 12volt accessory plugs, front, mid, or rear of vehicle work. The fuse in the engine compartment was blown & the new fuse shorted in my fingertips upon replacement. I didn't find any spare change in any of the sockets so I figured this had to be a chronic problem with a wiring harness plug or such. Thanks for any help!
 

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2002 chevy trailblazer_ls
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Discussion Starter · #5 ·
Yeah Rayvoy, I was afraid of that! F-Finger, there's nothing in any of the sockets. As for you ROADIE, I was hoping you would jump in on this, I have been a member for a little while & you have, along with a few others who need their horns tooted also, my respect when it comes to TV knowledge. As for the back fuse, I have a 2002 LS & assumed it might differ from yours slightly, I belive you have a 4x4, correct? After work tomorrow I will check the back fuses & manual for fuse #'s. The scary part is we all know how much fun it will be to track down a dead short!
 

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2004 gmc
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As for the back fuse, I have a 2002 LS & assumed it might differ from yours slightly, I belive you have a 4x4, correct?
Thanks for the kind words. The SWB all have pretty much the same schematics, and the differences in the 4X4 systems aren't affecting circuits like accessory outlets.

Dead shorts are every easy to troubleshoot, as a member allowed his mechanic to do yesterday. He turned a green wire's insulation black by jumping up an unfused 12V to it. :eek: :crackup: :excited: :rolleyes: :hopeless :suicide:

Seriously, it's possible to do if you have a power resistor or something that can limit the current to an amp or two. (like a 5 or 10 Ohm wirewound resistor). Hook that up in place of the fuse that's blowing. Now you have one or two amps (a safe current) flowing into the short. The 12V will mostly be dropped (dissipated) across the resistor, but some voltage will be left to be dissipated in the short.

Start tracing the wire from the fuse panel to the ultimate destination of the accessory outlet. With a good meter. All of my assumptions are that you own a good meter and know how to use it.

As you trace the voltage on the wire, let's say you start with 0.107 V (or 107 mV if you have a millivolt range) at the vehicle's end of the resistor. Moving to the bottom of the fuse block, you might find 87mV.
Near the accessory outlet, you might see 45 mV on the wire. At the point the wire connects to the socket you see 30 mV and spot the conductive contamination that's causing the short.

In another scenario, you trace the wire and underneath the dash a couple feet away, you see a junction, and the voltage there is 42mV. Then you go to the accessory outlet, and the voltage there is ALSO 42mV! That means the current (remember it's being limited to 1 or 2 amps) is NOT flowing on the wire between the junction (splice) and the socket you were measuring. This is known because current flow on a conductor ALWAYS causes voltage dissipation (a decrease along the wire). The skinnier the wire or the larger the current the more the voltage goes down as you go from source to destination.

That means the short circuit fault current is going down the OTHER leg from that junction. And you need to trace that wiring (with help from somebody with the schematics).

In your case, I'm betting a couple of beers that your problem is NOT in the accessory outlet in the dash, but in the secret little harness that brings the SAME power connection to the OBDII data link connector near the steering wheel. Where you plug in to read codes. Examine this connector and its wiring very carefully and you might find the short. Anybody been mucking about up under that part of the dash area recently?
 

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Discussion Starter · #7 ·
Ok, Roadie, you know what? uh uh! You no can ansah my questions one jeer!!! Kidding aside, I asked you what time it was & you told me how to build a watch, BRAVO for the extra mile! I will have a friend in electronics fashion the step-down gizmo (he has all that stuff lying around)to help locate the short if we first don't find it in the, um, "secret plug". I really do thank you, I was expecting to read point to point with a pair of 25' leads, HA! Oh, I do have a meter, & what kind of beer was that?
 

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I try. :eek:

Seriously my career in electronics was mostly in system design, troubleshooting, documentation, and training, besides mentoring the noobs. It's been interrupted for a bit with the downturn, so while I wait to get back to work, I adopted trailvoy to keep in practice for tech support and to collect a few attaboys along the way. Thanks for that.

If you've got an electronics buddy, tell him to make a floating AC shorts detector. Even cooler than the constant current gadget. This kind of gadget uses three probes to touch the wire of interest, to find out which DIRECTION the short is in. The middle probe tries to shoot a few milliamps of AC at 1-10KHz into the wire. Milliamps instead of amps in case it's an electronic component causing the short and you don't want to smoke it. AC because it's easy to tune a bandpass filter to match the stimulus frequency. And then you can amplify the heck out of the filtered detected signal (a few hundred microvolts, let's say) on either of the other two probes. The one where the short is will absorb (attenuate) some of the signal, while the one AWAY from the short will have the same AC amplitude as the source. With a few touchdowns of the probe, you can pretty quickly home in on the location of the short in a complex network of wires.

If your buddy is a high speed digital guy instead of a low level analog person, have him set up a high speed pulse generator, get a good sampling scope, and run a TDR of the wire you're suspicious of. That should be able to tell you how many INCHES away the short is from the pulse generator.
 

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2003 chevy trailblazer_ls
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Hey Guys.

I'm having the same problem as described above. I did have the codes checked last week and about 2 days later my accessory plugs stopped working. Are you saying the wires at the harness shorted? How is that possible?

Just curious as I'm about to take it apart.

Thanks!

Dale
 

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2003 chevy trailblazer_ls
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Specifically which ones stopped working? Only the main one is fed by the CIGAR fuse under the hood, which also runs the OBDII connector. Did you check fuse #46 in the rear?
Sorry. The one on the dash (front) and the one in the center console for the rear passengers have no power. The one at the back works fine.

I checked both fuses (#46 & #15, if I remember right) and both look good. I even bought new fuses and replaced both of those individually with no result. I looked at the one under the hood but didn't try replacing it.
 

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Sometimes, the little center contact gets pushed in and won't contact your plug. Do you have a meter to check for power getting to the center conductor?
I do. I'll check on that. I don't know if I've ever used the plug at the back of the center console before. I think I tested it when I bought it back in '07. The one on the dash I use all the time and this is the first time it's not worked.
 

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I do. I'll check on that. I don't know if I've ever used the plug at the back of the center console before. I think I tested it when I bought it back in '07. The one on the dash I use all the time and this is the first time it's not worked.
I tested both the plugs with a volt meter and neither show any life.
 

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2002 gmc envoy_slt_xl
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my 2002 XL SLT 4X4 has the same problem.... no accessory plugs work... keeps blowing the fuses..... but the cigarette lighter plug on the dash is fine....

post up if you find anything causing this problem.....
 
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