erock13

1986 4Runner 22re.. Out of nowhere my Tail fuse blew, and I have torn through the wiring looking for a short, only to find nothing.. I have disconnected everything on that circuit, taillights, marker lights, dimmer switch, and rear deck light .. Also all the rear window relays just for safe measure even though I have it all bypassed.. Without the tail relay its fine, obviously, but as soon as the relay makes contact with the pins, boom it's popped again.. I've also checked the grounds, all good, even cleaned em off real quick for good measure.. Only thing I can think of is that relay, possible corroded inside, is there a way to test it without buying another one? Or bypass it? Also checked the combo switxh, looks good.. No other issues anywhere else, just the Tail circuit..

RAD4Runner

Schematic is below.

Let's start with this:
1) By "disconnected" you mean disconnected the wires connected to the relay? or removed all the bulbs?
2) How about the license light? Did you inspect the flex cable between body and tailgate as well as the wires inside?
Also, please see signature.

In fact, the reason for testing the relay is so you would not have to buy a new one. We can go there after you answer questions above.

erock13

Forgot to mention that, the flex cable is completely disconnected and removed from the truck, no license plate lights back there anymore.. Everything except the front markers are disconnected via their plugs, the front markers just have their bulbs taken out..

erock13

Also no trailer wiring to deal with either

RAD4Runner

Please change title. Yotatech will solve it - LOL!

Tail light relay is upstream of the fuse. Any of its pin shorted to ground would not blow the tail light fuse.

Let's check...
1) Power off
2) Tail light fuse installed
3) Pull out the tail light relay. I believe it's the cylindrical one forward of the blinker relay in pic below ...
4) Measure resistance between bare, shiny metal of body ground and pin 3 of the relay socket. That's the pin with the red wire behind it.
Tell us what you see.

erock13

Lol, yeah i put unsolvable because ive been goin at this thing for 3 days now.. It's got continuity though, so that would mean the ground to ground is good correct?

RAD4Runner

What's got continuity?
Gotta describe describe symptoms and problems in EXACT terms. Pls see signature. Did you EXACTLY as I suggest above?

old87yota

Also, what exactly is disconnected from the circuit and what is still connected to the circuit?

You may get different readings based on what is connected.

If I am thinking along the same lines as RAD4Runner, you are looking to find a short circuit in the wiring and not knowing what is still connected could give you false readings.

erock13

Power was off, new tail fuse installed, disconnected relay, black probe to ground and red to pin 3 on the fuse panel, multimeter buzzed and gave a reading that varied between .03-.05 ohms

Coming from the rear first, the tails are disconnected at the plug, the harness that is supposed to go into the tailgate is disconnected at the plug, the cargo light is disconnected at the plug, the relays in the quarter panel are disconnected, the dimmer switch is disconnected at the plug, and the front marker bulbs are removed

erock13

I just realized that the alarm is also tied into the tail circuit, to flash the lights.. It's an aftermarket basic viper system, it's got two fuses and one of them is blown as well.. Was installed by a shop, so I'm not sure how it got wired up.. I'll try disconnecting it and see what I get

old87yota

Yeah, the alarm and how it is wired definitely complicates things from our end, as we cannot see how components are connected to the alarm system.

Hopefully the shop did a good installation job and not the "twist and tape" method.

Tell us what you find and if disconnecting the alarm changes anything.

erock13

The alarm led me to the issue.. Theres a split in the loom by the fusebox that carries either the tails or markers, not sure, but the split is for the alarm, and the fuse that was blown is connected to it.. Well that wire is partially hidden, it goes into the opening by the kick panel where the door switch is located, and then is bundled up with the door switch wires, well right out of eyesight was a portion that was kinked and had just the tiniest bit of exposed wire and was grounding out on the body, straightened out and moved away from the body, its back to normal. Thanks for the help guys, cant believe it took several days to find the stupid thing

scope103

Me, I'm impressed you found it that quickly!!

Good write up, lessons for us all.

RAD4Runner

Glad you found it. As I always stress problems are often caused by bad wiring (possibly caused by poor workmanship of the shop that installed your alarm) and/or maintenance.

Yep that^^^ right there indicates short to ground.
When we do things methodically, they become solvable

You insulated that wire, of course?

zuggie

This might sound crazy but I had the same problem /same troubleshooting/same results for 5 days (NO TAIL LIGHTS) but!!!
I noticed that the dash light bulb behind the defroster bezel had gone out. I replaced the light bulb-PROBLEM SOLVED!!!
Very small bulb comes in two wattage's. Use the higher wattage.
Z

acruet

I have a 5th gen 4runner (2016) and last night got pulled over for no tail lights.
fuse was blown, 10 amp under dash.
Removed both bulbs and fuse still blows.
What else is on that circuit that I can remove to be sure I don't have something as simple as a shorted bulb?
Does the third light (above in the spoiler) go on with tail lights?
Brakes and signals and hazards all work fine.
on Gen5 are the license plate bulbs on the same circuit?

In the headlight assembly everything seems to light fine.....

any clues will be helpful

thanks in advance

zuggie

I had all of my lights and dash lights working except for tail lights and brake lights. I was not blowing fuses.
After going through every circuit and replacing bulbs for three days I noticed that the dash light behind the bezel of the a/c/heater controls was out.
I replaced this tiny bulb and problem was solved. This tiny bulb comes in two different wattages if this is your problem use the higher wattage bulb.
Best of Luck,
Zuggie

acruet

Mine is a Gen5 and I found that the license plate lights and side marker lights (the amber ones) in the headlight assembly were also out.
Assuming these then are all on the circuit I decided to remove all of them to ensure the bulbs were not the cause.
It sux that to remove the side marker lights in the headlight assembly you have to gain access by removing the front bumper.
(What would Jiffy do if they tested lights and found one of these out?)
Anyway I pulled all of those bulbs (yes removed the bumper to get the marker lights) and the fuse no longer blew.
So I began adding each bulb one at a time and checking the fuse, and was able to re-install every bulb without blowing the fuse again.
I don't like saying the problem is solved, when I don't know what the problem was.
But I have all my lights back. I can only assume that the relay for that circuit got stuck in a weird status. When I turn on driving lights I hear the relay click.
So could it be that by taking the longest possible way to unload that relay, I allowed it to return to the right state?
If so I could simply have disconnected the battery to solve this issue.
We'll see how long the lights keep working.....fingers crossed

zuggie

Well. so far-so good.
Those bulb filaments are pretty fragile so a quality bulb would be in order.
Also, a dab of dielectric grease on the contacts would help in those conditions shown in your avatar. lol.
I regularly do a walk around checking all of my lights before I go out. "probable cause" can be a bitch.
Best to ya,
Sandy

acruet

So far so good. They are all still working.
Still don't know what the cause was.
Most of the bulbs involved are LED so low power draw.
The only exceptions are the marker (amber) bulbs in the headlight assemblies.
I am a motorcycle safety instructor, and we never ride without a quick once over all the lighting, and more importantly, tire pressures.

PS That snow was an unusual year about 5 years ago