Very Odd Problem- Right Taillight

Homebodyatheart

I have a 2017 320S. When testing my signals yesterday before towing my right tail light didn’t light up with the brakes on. However it does light up for the R turn signal and again for the emergency flashers. I removed the light and the three wires look to be in perfect condition, the storage cavity is spotless. We wiggled the connection at the TV, removed and reinserted it multiple times, it is properly lubed with dielectric grease, looks clean. No problems with any other tail lights/signals. Any other ideas and fixes? Thanks!

Horigan

Have you confirmed you're getting the correct signals from the TV receptacle?

On the front frame rail under the tub there is a junction box for the 7 pin connector.  You can confirm proper signals there to isolate whether the issue is in the 7 pin cable or the 320S wiring.

Bayliss

@Homebodyatheart, if I am reading your question correctly, the right brake light is the only light that is not illuminating.  In other words, the taillight, turn signal and emergency flashers are working.  Am I correct?

If so, I would check the 7-pin connections (tow vehicle receptacle and trailer 7-pin plug) to be sure both are clean and dry.  You will also want to look specifically at the pin connection for the electric brakes.  It's possible that there is some slight corrosion there.  Spray some electric connector cleaner on those connection and then follow it up by adding some dielectric grease.

Also, I agree with @Horigan's suggestion to check the wire connections in the wiring junction box on the front frame of the trailer.  Yours should be wired similar to my 2019 320 S, so check the #1 (far left) pin for the brake wire connections and the #7 (far right) for the ground wire connections.  Either may be loose.  You can see my wiring diagram for the junction box in this discussion thread:

https://tab-rv.vanillacommunity.com/discussion/10884/exterior-light-question

MuttonChops

Homebodyatheart said:
. . . right tail [brake] light didn’t light up with the brakes on.
. . . it does light up for the R turn signal and again for the emergency flashers.
. . . No problems with any other tail lights/signals.

I agree with @Horigan that you should check for the correct voltages at the TV 7-Pin.

It is difficult to think of any trailer reason for the Turn Signal & Flasher to function but not the Stop light.

For reference:

Homebodyatheart

Thanks for your quick responses and links. I’ve got some investigating to do… fingers crossed! I won’t be towing again until Monday, but I can play with it sooner. 

Dalehelman

Some vehicle tow packages include a separate fused area specifically dedicated to the trailer. So that if the trailer wiring malfunctions it will not effect the tow vehicle. It seems I remember seeing separate fuses for each Circuit. Including one for the left and right brake lights. Generally they are on the same circuit as the turn signal since they share the same bulb or LED. These fuses would be under the hood, probably on driver side. Or in the driver foot well area. Probably well out of sight. Check vehicle owners manual. For trailer towing and fuses. Maybe someone else has better Recollection.

Dalehelman

 If your wiring was done after market. The installer may have installed some sort of sub panel to prevent the chance damage to any of the electronics in the tow vehicle. If something go wrong with the trailer. Sounds like a good idea to me. Just brainstorming. If it were after market installed I would go back to them. This is a very strange problem.

Homebodyatheart

@Dalehelman it was after market, installed by the Toyota Dealer. I’ll check with them next week, and probably also call my usual car fixit guys at Tire’Rama. They are reasonable and usually can fix whatever I bring in. Thanks Dale!

Grumpy_G

On the trailer side there is only one connection running from the plug to the tail light, and there is only one "bulb" (set of LEDs) for both brake light and turn signal. If the turn signal works I can't come up with a scenario where the brake light doesn't. 
Does the Highlander have separate turn signals and brake lights ? IIRC the vehicle requires some sort of module to properly drive trailer lights. As already suggested make sure the tow vehicle puts out voltage on both the left and right turn/brake pins (3 and 9 o'clock position from the notch). 

Dalehelman

We already know the light is getting power. Because the turn signal and the emergency flashers work. There must be something in the TV that is separating the brake light circuit. Generally when trailer lights do strange things it can be traced back to a bad ground. But I don’t think so in this case.

Dalehelman

Put a test light on the 3 o’clock and 9 o’clock from notch of the seven pin of the tow vehicle. If they both light then it must be in the trailer. If one doesn’t light then the problem is in the TV. Ground the test light to the vehicle frame then use the probe on each of the  fore mentioned terminals. 

jtalarek

I had a similar problem with the right tail light; the turn signal and brake light did not work but running light did work.  It was a bad light, installation of new bulb did the trick.

Dalehelman

Most foreign cars have separate brake and turn signal lights. American trailers don’t. There is a module generally near the 7 pin that adapted the foreign wiring to the American. That could likely be the problem. It is fairly cheap and easy to replace 

Dalehelman

This is my guess as to what is malfunctioning.
You just cut off the flat four plug and reattach the wires to the 7 way.
I want to recommend this product at Amazon<BR><BR>CURT 56130 Non-Powered 3-to-2-Wire Splice-in Trailer Tail Light Converter, 4-Pin Wiring Harness<BR>by Amazon.com<BR>Learn more: https://smile.amazon.com/dp/B0049CI05W/ref=cm_sw_em_r_mt_imm_awdb_8RCS3NV9G1VGYDMJH6CV

MuttonChops

@Homebodyatheart ;

Has this been resolved - - repair delayed - - working on it's own now ? ? ?

Dalehelman

I talked to homebody a couple of days ago. It is apparently working fine now.

Dudlee

   Intermittent electrical problems are a real drag unless you own an old Triumph, MG , or Jaguar. You learn to love them then. :}

Homebodyatheart

Thanks Captain @Dalehelman for the update! @MuttonChops sorry for the radio silence… I had an odd light when I plugged it in to head home, so I unplugged it and made sure that this time I inserted the plug in straight and all the way. Voila! It worked like a charm! I think the original problem may well have included “operator error” from my crew person before I left home. It looks pretty clean and still has a fair amount of dialectic grease in it. I suspect investing in a cover cap might be a good idea! Thanks again to everyone for your help! I learned some new things in all this( and will probably plug it in myself next time…)

TabulatorJim

In getting our 2018 Tab 320S ready for the season, our left back turn signal and brake light did not work. As the countdown to travel was on and we sought forum advice, we assumed it may need replacing, we ordered a new one, the Kaper II L15-0021 Red LED Trailer Turn Light, from Amazon. 

Preparations were made and further tests conducted. Taking the old one apart and checking it for rust and loose wires, it looked as if replacing this may not prove difficult.

While waiting for its arrival, we sought advice from someone we trusted. We took our unit to Sunwest RV Centre here in Courtenay on Vancouver Island, where we purchased this, and spoke with Erik Vierstra, the service warranty advisor. He went over a series of procedures to see if we could isolate the problem. In order, he is what happened:

1. As the tow vehicle lights all worked, he advised tracking the problem from this on back. He tested the brake/light connector. No problem was found.

2. Next, Erik recommended using dielectric grease (as was suggested by ericnliz in 2017) on the brake pins. I purchased a very small tube of this from Lordco Auto Parts and applied this using Q-tips without success.

3. Just prior to travel, the replacement light arrived and there was no time to install this. As a last ditch effort, I decided to give the dielectric grease a final try. This time, I cleaned deeper and much more thoroughly – it worked!

We all lit up and had a great holiday.

Hope this helps others enjoy one too.

Cheers,

Jim