Electrical Help wanted - Finding a "dead short"!

[tay_ninh]

I am not exactly sure of what I am doing, so, here goes! Had some mice in the 2015 highlander but now have them trapped out. Don't know if the mice ate thru the insulation somewhere or if something else happened. Anyway, We went out to the vehicle one night, and just noticed that when we opened the door, we had NO lights, then noticed that none of the interior lights were coming on. Checked the fuses. The fuse box, drivers side, under dash had a 10 amp fuse blown, says "Dome". Ok, I'll get another fuse. Put the fuse in and INSTANTLY, the fuse blows again. Hoping for a cheap fix, I bought a replacement 10A fuse that will reset itself and put it in a series with a light bulb and hooked it up to replace the actual fuse. When hooked up, the bulb instantly lights up (indicating a short), and the relay starts making a buzzing sound. So, think that is called a "dead short". Next thing I did was disconnect the neg battery terminal and hook up one of those "short tester" that look like a screw driver with a light in the handle to the neg terminal. I took out every bulb in each light, and touched each terminal in the light with the short tester. I went front to back, and every one looked good to me (handle lit up for both terminals when contact was made) until at the back (the luggage area) and only one side showed voltage. The two wires are sky blue on lavender (showed voltage), and green on lavender (no voltage) so, I presume the green on lavender is shorted out somewhere in the harness because it is not showing voltage at that point. Now,,,,,,,,,,how do I find the "actual spot where it is shorted out" The wires are in some kind of plastic tubing. I took out the back flooring where some of the wires are, and checked that lavender/green wire, and everyplace I checked so far, is showing nothing. It looks like I might have to take out the seat, and side panel to get to the other wires,,,,,,,,,,,,,,,,,,,,but I don't want to do that if I don't absolutely have too. What is your opinion? Am I looking at the right wire? Do you know of any other way I can find where it is actually shorting out? Thank you very much for any help you can give me!

[Ol'fogasaurus]

Can you go to each end of the "green on lavender" wire so you can do a capacitance check?

[GS guy]

Some vehicles a number of years ago were assembled with wiring insulated with some kind of corn-based plastic material - a favorite rat food! I'd start by crawling underneath the car and checking any wiring harnesses you can trace looking for "chewed away" areas. Under hood too. It'll probably be fairly obvious when you finally find the chewed insulation/wiring covering. This happened to both my son's Acura and MIL's Honda. Hardest part may be just getting to the wiring to check it - engine compartments are so full of "stuff" these days.

[tay_ninh]

I looked at all the wires I could get to and found nothing visually. I checked the wires for voltage near where the inside lights are located, and found nothing wrong. It is still drivable, just don't have interior lights, so been taking my time and trying to find it.
Well, I now have a "new twist" on my short. It doesn't seem to be a dead short now. It seems to be more intermittent now. I know, it sounds crazy. I had hooked the 12V bulb back up to the fuse box,,and the light came on indicating still have short. I was fooling with the on/off buttons on the overhead interior light, when all at once the light went out, indicating I had found the short. I took out the socket, and while moving it around, the light came back on (thought for sure I'd found the source of my short). Then unplugged it from the harness, and while still disconnected, I touched the wires sticking out from the harness, and the light came on again. So, thought it was in the overhead wires. Now the crazy part, while standing there, without touching anything, the light would go out. Then I would hear a clicking sound a few times, and the light would come back on. (without me doing anything). How could this be? A question: If I remove the whole light socket from the harness (disconnected at the plug) should the other lights work, in this situation. OR, would I have to have the socket plugged into the harness?

[Ol'fogasaurus]

Do you have fuses or just what? Have you taken the switch out and played with it to see if it has a bad or loose internal connection? Your capacitance checker should do that. Also you might check the feed to the switch too.

Just a start on tracing down electrical problems.

Lee

[tay_ninh]

Hi Lee, yes, it has a (under dash fuse box) a 10 amp fuse that was blown. The fuse box is attached under some kind of black "computer type" box called MPX Body on driver side. Regular fuses blew "instantly" when inserted. Bought one of those testing type fuses that reset themselves, instead of blowing regular fuses. Put it in a series with a 12V bulb, and attached it to a "blown fuse" (on each side of the fuse) so I could insert it into the fuse box. Supposed to act opposite of a fuse, so when I put it in place, the light comes on indicating a short. I complete pulled the overhead light assbly, where I was fooling with the switch, but then found that the test light would come on and off when I touched the wires. So, we are standing there by the drivers door, and the light goes out (without us touching anything) so, then we keep watching and the light goes back out (again w/o moving anything) after a while we hear something clicking, and then the light comes back on (again w/o touching anything) ALL BY ITSELF. How could that be possible? We still have the overhead assbly out, so that should rule out the switch?

[Ol'fogasaurus]

It is the "clicking" sound that bother's me.

Normally if a wire had a bad connection or internally the wire was broken or something like that you would be less likely to hear a "clicking sound" unless it was supporting (maybe) another in-line something such as a relay for something else that has been tapped into that wire. Even a bad connection prior to a fuse could cause what you are describing. The same thing could happen with a bad ground wire or it's connection.

Have you been able to locate the area that the clicking sound is coming from? It sounds so simple but that location might be a clue to what is going on.

One of the reasons I recommend using a volt/OHM meter as they are not drawing that much power, just reading what is happening.

Wiring isn't always easy is it.

Lee

[tay_ninh]

It's called a body control unit,,,,,,,,,,,,,,don't know what it's functions are. Would post a picture, but can's see any way of doing it on here. I'm starting to think it is something wrong in the Body Control Unit.

[tay_ninh]

No it isn't,,,,,,driving me crazy. The "original" buzzing (I guess was caused by the self resetting fuse). I could feel a slight vibration when touching the side of that body control unit, similar to, but not as much, when you are holding an electric razor? As I said before, this was a steady buzz, and the light was on indicating a short.
Now, after moving some of the wires and unhooking overhead light assbly, the light will come on, with the constant buzzing, then, automatically, the light goes off, the buzzing stops. Then, after about 15 or 20 seconds, I hear a click,,,,,,click,,,,,click (which seems to be coming from under the dash, over the area of the accelerator), then the light comes back on and the buzzing starts again. This seems like it would just keep doing this over and over if I didn't pull the testing fuse out of the fuse box. A short is usually a short,,,,period, and doesn't go on and off unless a wire or something is moved, that is what is so crazy. In the beginning, that WAS the way it was,,,,,,,,,,but then after fooling with it yesterday, it started the on/off/on pattern. I going to go now and see if I can find where that "new" clicking sound is coming from.

[Ol'fogasaurus]

Never heard of the term before but the concept is interesting.

https://www.bing.com/search?q=what+is+a ... f91c652bc0

Lee