Trailer light connection issues

Hey all.
Something weird is going on.

Using an led plug tester.
Without brakes applied, Trailer blinkers only work if the tail lights are OFF. Unless the brakes are applied then they blink along with the tail glow.

The second the taillights are turned on the blinkers quit unless the brakes are on.


The trailer wiring appears to be extra jacked up. Im only getting a left blinker unless the tail is on then i get nothing. Said left blinker does not operate only as a brake.


I could be dealing with a bad ground In the truck?

Something shorted in the factory trailer converter box under back seat?
Blown fuses to said converter?

Any thoughts appreciated

 

I do know the factory trailer lights box was a piece of crap.

If your trailer plug is not corroded and bleeding voltage to another pin, you can reasonably assume the trailer light box is bad.

I've had 2 out of my 3, 1st gen Tacomas do this.

 

2nd on the converter box!!

 

Not entirely surprised
Do you have any suggested alternatives besides simply replacing the box and expect to replace it again in another 20 years?

Id rather not hack into the wiring under the bed and add an aftermarket box

If i had a schematic to hack an aftermarket box in the location of the oem one i would be much fonder of the idea

I may poke around and figure it out without a schematic too

All wires and connections Look 100% ok


Hilariously the trailer wiring is completely crapped out at the same time as the truck having issues. Found out why the right side was definitely doing nothing. Both hot wires rotted off at their crimp connections. (Definitely not related to the taco's own drama)

 

Sooner or later all my vehicles get 7 pin plugs

Even if itis just for fixing trailer lights and brakes.

You should be able to get the light schematics from someone.

 

Find and inspect all of the grounds too: especially the trailer wiring related ones, but all of the others as well. Bad, sketchy/rusty or broken grounds can cause all kinds of strange electrical problems: like brake lights on when you turn on the headlights, blinkers making taillights blink dimly, etc.

 

Everything on the truck Looks great
The ground goes all the way back to the converter box by the looks of things

 

Hopefully this was not a bad idea
I bought a "new" oem module from ebay. I was sent a warning from the seller.....

Please be aware this is not a self-install plug and play item. At a minimum, it will require body control reset using ob2d scanner. It may require TechStream Toyota Lexus software depending on the issues your vehicle has.


Is this guy correct?
Why the hell would a trailer converter need to be programmed and matched to the computer?

Is it gonna be a total nightmare?

 

I have never heard this with a truck of your age .

Good luck

If you bought a converter box.

It only works for the lights any other effects will be up stream from converter box.

 

Take the trailer out of the equation and check voltages at the truck wiring connection at the bumper your test light or with a DVM. I thought I fried my converter back in 2002 when the truck was new doing a little trailer wiring so my friend at Toyota got me a new one under warranty. Turned out to be a fuse below the converter so still have a new one in the box.

 

Fixing trailer lights is a on going job though Led's have made it mostly wiring and connections

 

Yea the trailer wiring was its own separate nightmare that as of yesterday has been freshly rehashed and might be good for at least a minute and a half. Im about to put crinkle tube on the wires so maybe theyll last about 2 minutes.

The truck's issues are real as confirmed by the test plug. The fuses dangling from the harness at the converter under the seat are intact

I also cannot imagine this guy being correct about the module needing to be keyed to the computer but what do i know

 

The tester results really sound like a bad ground pin connection on the truck side of the trailer connector. You are borrowing the tail lights as a ground when they are not on.

I have not had any problem in my Tacoma with the factory 4-pin trailer wiring harness adapter but I don't tow all that often. I bought the wiring adapter and the receiver from my dealer and installed it myself back in 2004. I did not have to do any sort of reset procedure. I disconnected the battery while installing the factory trailer wiring and reconnected the battery when done, and everything has worked fine since. (2004 Tacoma, base model 5-lug)

 

Bad ground... this has obviously crossed my mind but i know not where to start looking. Weird crap happens with a bad ground.

I wish in a way that said ground was out there and visible (yeah right it would be rotted off) lol. Guess ill have to poke around

Id expect the converter box to eliminate the ground loop through the tail lights but i guess weirder things could happen

 

Hokay
Its not a ground issue. I just made up an extension with an auxiliary ground wire grafted in that i hooked directly to the battery. No difference. Flashers work alone
Tail only if its on
Unless the brakes are on. Then everything acts normal
Seems like the blinker-power circuit is confused.
The blinker-brake interrupt circuit is still solid

It seems like the converter has to be at fault. New one will be here soon.

 

....
Im just confused and becoming pissed off lol.
I just fully rewired the trailer. Soldered joints. Know i hooked em up right. Tested the lights before i put it together. I know they do things.
Well all i get is a left blinker. Nothing else does jack. Not even matching the test plug.... i have the ground jumper to the battery to no avail... uy

 

After 40 years I learned to go with the flow.

At any time did it ever work correct ?

Clean the sockets check the bulbs with a meter ..

This is why I convert every trailer to separate turn signals like the Toyota Tow vehicles.

 

Becoming has became.
This is a living nightmare

Of course it already has the squirrel shield installed. Was a bitch in a boat to put on.

They are led. I wont use anything else anymore.

Separate turn signals on the trailer.
Ok cute.
Are you misusing a 7 pin plug?
Even those intend for the lights to be combined

....
The left blinker. Only. Ever.
Only from the truck.
Trying to do some diagnostic with a known good battery. Testing at 12.65v. Sparks gleefully when i bang the jumpers together.
I tried touching the plug. Nothing
Tried cutting into the wires in doubt of the plug. Nothing. Multimeter says the plug is fine. Hang the jumpers on the cut-into trailer wires. Nothing. Yet the left blinker was blinking merrily from the truck.

All lights tested good before i rewired it
The wires are double twisted and soldered. Nice solid joints. No cold solder. No crimps. No twist and forget
Ground wires directly to the lights... no shitty rusty ground through the shitty rusty frame. I know for a damn fact i hooked em up where they need to go

At this point im just ranting
This is a tacoma forum not Your Grandpa's shitty boat trailer that has been turned into an extra-shitty utility trailer forum...

Im glad i didnt wait until the last minute when im headed from kentucky to arizona in march for my wedding and to drag back my old deathtrap of a motorcycle

Uy. The shit saga continues.
I may have to get new lights?
Despite seemingly being OK?
UY

 

Sounds like you're working on a new problem, trailer wiring now. If you have the truck side of things fixed, that's progress!

 

I would say have someone else hook to trailer to see if it functions properly. This will tell if it's the trailer.

On the other hand, my truck was not lighting trailer on passenger side sometimes and sometimes it did. I replaced the harness with the one below and have had no issues in 2 years.

$55 Curt Manufacturing 55379 Vehicle-Side Custom 4-Pin Trailer Wiring Harness,Fits Select Toyota Pickup,Tacoma,Black

https://www.amazon.com/dp/B0009I5WK6?language=en-US

Hope this helps.