Trailer lighting problem!

So, I am preparing to make a trip next week with a car hauler trailer. First time towing a trailer with this new Taco.

I got the trailer brake controller installed, no problems. I tested that and confirmed the trailer brakes are working properly.

Here’s my problem: the turn signals on the truck or trailer do not work when the trailer is connected. I thought it blew a fuse, but when I disconnected the trailer, everything worked again without any fixes. I thought I was crazy, so I plugged in the trailer again, and the turn signals went out.

Anyone else experience an issue like this, or know what might be causing it? The trailer I am using works fine on a couple other vehicles, and I know it. I used it last week on another truck (of another make) without incident.

 

I locked the plug in with the lid. The turn signals stop functioning on the TRUCK and trailer both when the trailer is connected. The dash light showing the turn signal doesn’t even light up.

 

I am going to ask, did you happen to test the lights before installing the brake controller?
That would be nice to know if it was like that before the install or only happened after the install, then you will know what direction to take.

 

My only working theory so far is that there’s too much current draw on the flasher with the addition of 3 more bulbs and it refuses to flash.

I’m going to disconnect the trailer brake controller and try again.

 

I think it has a circuit protection in addition to fuses, because mine doesn't blow the circuit when i put my shitty trailer in salt water...
I put my money on a short in the trailer to ground.

let me look at the schematics.

 

I would say operating the turn signals appears to be an electronic decision by the combination meter, looking at the schematics. Flasher relay function looks to be 100% in the combination meter, with separate wires running to normal lights and to the trailer from combo meter. I don't have any internal schematics for the combo meter.
I think its a short in trailer wiring or plug.

Stop and tail lights work on trailer?
An interesting test would be to try the hazards with and without the trailer, but be warned the combo meter may not provide as much protection on the hazard circuit, due to fail-safe conditions. It might blow a fuse.

First thing I would do is try and use ohm meter to check the resistance to ground of the trailer at the plug... my first guess to try...

 

So I tried it on the same trailer, and a different trailer with fewer lights. Looks like my hypothesis is true.

The original trailer works fine hooked to a different vehicle, but causes my turn signals (and brake lights) to die. Running lights are okay. When I disconnect that trailer, everything works again.

A different trailer with fewer lights works fine hooked to my vehicle.

Why is there a limit that nobody knows and isn’t publicized anywhere?

 

Is the trailer LED or incandescent?

 

I could not find any mention of a limit in the service manual after looking pretty hard. The owners manuals are longer than the Toyota repair manual for Toyota Pickup I had, yet seemingly no mention at all, wtf.

From looking at schematic yesterday, (from memory) I thought brakes used a different circuit from turns, not routed thru the combo meter, hmmm have to look at that again tonight.

We talking 4 pin connector or 7 pin that you are noting the issue?

That brings up another question, I don't know where brake/turn integration for 4 pin wiring occurs, off my head i would think inside the 4pin/7pin connector on the truck.

 

It’s 2 incandescent per side and one LED per side for a total of 3.

I am using the 7 pin. There’s no way it can combine the signals inside the connector, it must be done by the BCM because the flashing is synchronized (if you do the old fashioned diode bridge method you get alternating flashing between truck and trailer lights when the brakes are applied at the same time).

 

Poor trailer ground

 

I think you are right, now that I think of it, I am pretty sure it's synchronized on, not out of phase even on 4 pin.

Damn wish brought the schematic data to work, not doing anything right now and that would be interesting to look at...

Be interesting if you removed bulbs till it worked...

 

The trailer I was using is at the farm, won't be able to see it for a few more days. I can't easily start unplugging bulbs....but I do know that 2 incandescent (and one LED) were too much, but one incandescent (different trailer) was fine. So that is the bounds of working/not working.

 

I really can't remember where I saw this, but there's something to do with the number of LEDs vs incandescent bulbs in the truck and trailer that makes the blinkers and brakes go haywire.