CHASING DOWN A SHORTED WIRE

Having problems with your vehicle? Or need advice on repairing or servicing your Hilux? This is the place to ask for help
Post Reply
JAMES399
High Range 2WD
High Range 2WD
Posts: 25
Joined: Tue Jan 24, 2017 3:21 am
Town: Alejandria Antioquia Colombia SA
Vehicle: Toyota Hilux 4x4
Real Name: JAMES

Fri Feb 02, 2018 5:46 am

A while back, my '03 Hilux 4x4 unexpectedly blew a fuse in the taillight circuit. This circuit controls the dash lights, taillights, and license plate lights. I replaced the fuse, and it worked for a few days and blew again. I hooked an ohmmeter into the circuit, and it looked normal. So I took the truck for a drive on our rough dirt road with the meter connected, and every so often it showed a dead short.
I decided to try and figure out the problem. I have a downloaded Hilux manual. It took me several days to decipher their schematics, but I started out by opening up the relay and fuse box under the hood. This is where the taillight fuse is located.
fuse and relay box.png
This is the rat's nest I found when I finally figured out how to open the box. The wire from the taillight fuse had gotten hot, and was fused to several other wires. I separated them and it looked like none had shorted. Just to be on the safe side, I ran a new wire from the box to the junction box inside the cab. This was a real ordeal, because figuring out what went where in the J/B using the Hilux manual schematics was almost rocket science.
junction box and integration relay.png
Took the truck on another drive, and the short still showed up intermittently.
At this point I panicked. If the short was under the dash, it would be hell to find. So, I started at the taillights and worked forward. I removed the passenger seat, lifted the carpet, and disconnected the junction connector to the rear lights.
rear wire loom.png
rear wire loom.png (308.63 KiB) Viewed 206 times
rear harnessUntitled.png
Another drive showed that the intermittent short had disappeared. Checking the resistance at the terminals in the junction connector showed several wires were very close to ground (less than 2 ohms.) At this point I removed the taillights and the license plate lights and a recheck showed the low resistances were still there. I unwrapped the front part of the harness and found the taillight wire and its ground wire had gotten hot and were almost completely fused together. It looked like I needed to pull the entire rear harness, and this meant removing the gas tank.
Finally got the entire harness out and unwrapped. Three wires were completely fused together: the taillight power wire, taillight ground, and left hand turn signal power. I replaced these wires, rewrapped and reinstalled the harness. Everything checked out ok, and after 2 weeks, no more problems.

It took me 1/2 hour to do this writeup, but almost a week to find and fix the problem. A lot of work, but on the plus side I now have a real understanding of my Hilux's electrical system and I know how the Hilux manual works too.

- JAMES

Mars
LR4WD, Lockers, Crawler Gears
LR4WD, Lockers, Crawler Gears
Posts: 1214
Joined: Mon May 07, 2012 12:33 pm
Town: Pretoria
Vehicle: Toyota Hilux 3lt D4D DC 4X4
Real Name: Marnus

Fri Feb 02, 2018 6:37 am

Congratulations on sorting out this problem. Most guys would simply take it to the auto electrician. Do you have any idea why this happened?

User avatar
Mud Dog
Moderator
Moderator
Posts: 28374
Joined: Tue Apr 29, 2008 2:18 am
Town: East London
Vehicle: '90 SFA Hilux DC 4X4, Full OME, 110mm lift. Brospeed branch, 50mm ss freeflow exhaust. 30 x 9.5 Discoverer S/T's on Viper mags. L/R tank. (AWOL) '98 LTD 2.4 SFA, dual battery system. Dobinson suspension, LR tanks, 31" BF mud's.
Real Name: Andy

Fri Feb 02, 2018 8:28 am

Glad to hear that you got it sorted! :thumbup:
When your road comes to an end ...... you need a HILUX!.

Image
Image

Life is like a jar of Jalapeño peppers ... what you do today, might burn your ass tomorrow.
Don't take life too seriously ..... no-one gets out alive.
It's not about waiting for storms to pass. It's about learning to dance in the rain.
And be yourself ..... everyone else is taken!

JAMES399
High Range 2WD
High Range 2WD
Posts: 25
Joined: Tue Jan 24, 2017 3:21 am
Town: Alejandria Antioquia Colombia SA
Vehicle: Toyota Hilux 4x4
Real Name: JAMES

Fri Feb 02, 2018 4:09 pm

Mars wrote:
Fri Feb 02, 2018 6:37 am
Congratulations on sorting out this problem. Most guys would simply take it to the auto electrician. Do you have any idea why this happened?
Yes I do. The previous owner evidently towed a trailer and had a wiring harness connected (I could see where he clipped it out). This must have overloaded the circuit, because he had installed a 30A fuse when it called for a 10A. The extra current draw heated the wires to the point where the insulation melted and the wires shorted.
But this is a Toyota problem too. They use 20 ga wire throughout the harness. 20 ga won't handle much over 10 amps, so there isn't any safety margin if you want to install extra lighting, accessories, etc.

- JAMES

Post Reply

Return to “The Workshop”

  • Information
  • Who is online

    Users browsing this forum: Bing [Bot], Google Adsense [Bot]