New XLT Shorted Circuit

[svfetter]

I know I can take my new XLT in under warranty but just wanted to see if anyone had any thoughts.

There is one 10amp circuit on my 2011 which powers - Glove box light, Visor mirror lights and individual Dome lights. Fuse was blown when purchase and will instantly blow now.

I have removed all Visor lights and unplugged glove box lamp and the circuit is still shorted. Dome lights will work thru other circuits.

While this particular circuit is not that important, my fear is that the short is deep in the trucks wiring somewhere and will be near impossible even for a tech to find. My tests so far would seem to confirm that.

Any other ideas ???

 

[Captain Morgan]

I think any decent tech with a voltmeter can check continuity from the bulb sockets and see of he gets grd on both terminals. If he does on all of them, then the short is between them and the fuse box. If only one of them, then focus on that harness etc until he figures it out.

 

[svfetter]

I think any decent tech with a voltmeter can check continuity from the bulb sockets and see of he gets grd on both terminals. If he does on all of them, then the short is between them and the fuse box. If only one of them, then focus on that harness etc until he figures it out.

I think you are exactly right. I just wonder as complicated as cars and trucks are today whether the short could be somewhere in the truck where you cant get to it.

I will try to isolate the circuit myself with the volt meter.

 

[Thermo]

svfetter, I am placing money that one of your visors has a short in it. Not an uncommon thing. After that, I will venture to guess that your dome light has had someone mess with it and they managed to ground the power wire to the body of the truck by not routing the wiring inside the truck properly. So, what ended up happening is they screwed a screw through the power wire, leading to the direct short. After that, look at the bulb bases and see if any of them show signs of heat damage from where someone may have tried to get more light by using a higher wattage bulb. Would not be the first time I have seen that.

 

[svfetter]

Last night I tested each visor light and the glove box wiring socket and found each had an open circuit.

Does not make sense to me but when connecting my meter to each positive and negative in each location my meter showed no short in that line. I certainly thought one of the (4) visor bulb sockets or the glove box socket would read as shorted on my meter but none did. Not sure how I can check dome lights as they work when doors open or when you turn them on at the dash. But will not come on when you push click them for individual operation.

Thermo, you may be right about a screw being run into wiring somewhere. Not being an actual electrician, I am at a loss as to how I could pursue any further.

I am glad that this particular circuit is not an important one as I think It could be a nightmare to find.

 

[Captain Morgan]

Yup, screw in the harness or wire was nicked pulling it through somewhere.

 

[Thermo]

SVFetter, what I would tell you to do is to find the interior light relay and then probe the output terminal inside the fuse box to chassis ground. Make sure to remove all the bulbs before doing this. You should have an infinite resistance reading. Granted, anything more than say 100K ohm is more than adequate. If you have something in the 5 ohm or less range, then you have a power wire shorted to ground. At this point, you can start unplugging the various light fixtures one at a time till the ground goes away. The last thing you unplugged is what is giving you your problems. If you can unplug everything and the ground is still present, then the problem lies in the harness itself and the only way you will find that issue is to hand over hand the wiring harness or be able to get your hands on a TDR meter (just a little hint, they are like a $5000 piece of test equipment, so, unless you have really rich friends who are techno geeks, you will not find it). If the harness checks out good, then you can start adding in light bulbs one at a time. If I remember right, each of the bulbs are 5 watt bulbs. So, inserting 1 bulb will drop the resistance down to around 25 ohms. As long as the resistance is not dropping below 10 ohms, then consider that light fixture good. Remove that bulb and install a bulb in the next fixture. Check again. Repeat until you have checked all the fixtures. At this point, if you can pass all of these checks, then your problem is the relay itself. The only other option is to swap the interior relay with another one of similar rating and then see if a different fuse blows.

Hope this helps.

 

[ELVATO]

Hah, I would have taken it back to the dealer and have them mess with it under warranty.

 

[svfetter]

SVFetter, what I would tell you to do is to find the interior light relay and then probe the output terminal inside the fuse box to chassis ground. Make sure to remove all the bulbs before doing this. You should have an infinite resistance reading. Granted, anything more than say 100K ohm is more than adequate. If you have something in the 5 ohm or less range, then you have a power wire shorted to ground. At this point, you can start unplugging the various light fixtures one at a time till the ground goes away. The last thing you unplugged is what is giving you your problems. If you can unplug everything and the ground is still present, then the problem lies in the harness itself and the only way you will find that issue is to hand over hand the wiring harness or be able to get your hands on a TDR meter (just a little hint, they are like a $5000 piece of test equipment, so, unless you have really rich friends who are techno geeks, you will not find it). If the harness checks out good, then you can start adding in light bulbs one at a time. If I remember right, each of the bulbs are 5 watt bulbs. So, inserting 1 bulb will drop the resistance down to around 25 ohms. As long as the resistance is not dropping below 10 ohms, then consider that light fixture good. Remove that bulb and install a bulb in the next fixture. Check again. Repeat until you have checked all the fixtures. At this point, if you can pass all of these checks, then your problem is the relay itself. The only other option is to swap the interior relay with another one of similar rating and then see if a different fuse blows.

Hope this helps.

Thermo,

Thanks so much for trying to help. I am not dumb but I am not an electrical expert either. I am not sure I understand how checking the relay will help.

Just to review, The circuit in question only has (3) items on it - Glove Box, Visor Lights, and dome lights. The dome lights work on all other functions except individual push on.

I have removed all visor lights and unplugged glove box light and fuse will still instantly blow. I have an inexpensive meter and when I check each empty bulb socket they show an open circuit. I have not removed the dome lights simply because they work on all other functions.

I would tend to agree with you that the problem seems to be deeper in the wiring somewhere. Forgive me for being redundant but I just wanted to respond in detail again since you were kind enough make a suggestion.

 

[Thermo]

svfetter, I think in your case, how I would troubleshoot this is to first get your hands on a few of the correct size fuses. Now, unplug the dome light, disconnect both of the visors, and then unplug the glove box lights. In short, if it is a light on that circuit, remove it at the plug, not at a the bulb base. Now, install a new fuse and open a door to make the circuit turn on.

Did the fuse blow? If yes, then remove the relay and install a new fuse. Does the fuse blow now? if yes, then you have a wiring problem inside the fuse box. More than likely a new fuse box will be in order. If the fuse did not blow, look on the relay. You will see posts labeled "30" and "87". I want you to cut a small piece of wire and stick it in the slots where these two pins would go. Does the fuse blow now? If yes, then you have a wiring issue inside the dash for the light circuit. Probably time to take it to a shop to have them fix it since this is going to be out of your field of expertise. If the fuse has not blown at this step, continue.

If on the initial check of the fuse it did not blow or for some reason the above checks did not result in a blown fuse, plug in the lights one at a time, checking the fuse each time. The item that blows the fuse is the one that has a short in it. Unplug what blows the fuse, install a new fuse, and then continue plugging in the rest of the lights till they are all plugged in and the one(s) that cause the fuse to blow are unplugged. From there, you can replace/repair the individual component since you will know the culprit.

I do not necessarily like troubleshooting this way, but sometimes it makes things a lot easier.

 

[svfetter]

Thanks so much thermo,

I am going to do my best to try to go thru your method. However I did not find a relay that I could identify which controlled these circuits.

When I get a chance I will print out your instructions and give it a try. Noting to loose. And If I can't fix, maybe I can at least point the dealer in the right direction.

 

[svfetter]

Hey Thermo,

Problem Fixed !!!!!!! Don't ask me how. This is what I did. I did pull the fuse for all interior lights. (Dome) Fuse (Circuit) would still blow.

Identified circuit as Lt Green and Yellow Wire. Removed main Wire Harness with this color wire from fuse box. Fuse did not blow. Replaced, Fuse blew. Removed and replaced all other smaller harnesses which attached to fuse block but none of them had a Lt green / yellow wire. No Change.

OK, Going to remove visor from ceiling and see if I can unplug each separately to isolate. No Such luck. Removed each visor and found one incased cable with a black an red wire. Just a small amount of slack and no way to disconnect. Wires were not damaged to look at them. Repositioned wiring to extend into roof opening and reinstalled visors.

Just for the heck of it, tried the fuse one more time. Circuit is for 10 amp. Installed a 5 amp. It did not blow !!!!! Plugged in Glove box light, it came on. Reached up and pushed dome light. It came on. And one by one I reinstalled the lights into the visors and one by one they all came on. Circuit is currently working fine...

Not sure where the problem was but I must have affected at some point in the process. Based on what I did I don't thing the problem is deep in the truck as least. Thanks for your help.

 

[Thermo]

svfetter, I would venture to guess that you have a pinched wire bundle somewhere and when you were messing with the black/red wire, you moved the bundle enough that it is no long being pinched, leading to the short issue. Keep an eye on things and go from there.

 

[Notmyidi]

I'm voting short to ground, if you ohm between positive and the body and you find high ohms, you have a short to ground probably between the fuse box and the first bulb

If you read ol or the sideways 8 it means no short

Power has to be disconnected, since the fuse is blown you'll be fine

There's another test but I'm not gonna recommend it, do it wrong and **** goes your wiring

sent from my mind via of telepathy

 

[Notmyidi]

Ohm it at every accessory

sent from my mind via of telepathy

 

[svfetter]

Thanks Guys - Everything still working great !!