CHASING DOWN A SHORTED WIRE

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.

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.

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 (308.63 KiB) Viewed 3 times

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