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!
2017 T@B 320 Max S silver and cherry red, L@dybug ("Bug" aka my esc@pe pod), TV 2015 Toyota Highlander aka Big Red
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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.
2013 Toyota Highlander 3.5L V6
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
(Alde: 3020; Refrig: Isotherm Cruise 65 Eleg; Battery: BB 100Ah LiFePo4; Solar: Renogy 100Ah Suitcase; Victron BMV-712; Pwr Cntr: PD-4135KW2B; EMS: PI-HW30C)
Greg & Marlene (Tucson, AZ)
It is difficult to think of any trailer reason for the Turn Signal & Flasher to function but not the Stop light.
TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
Adventures: 51 Nights: 322 Towing Miles 41,200+
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).
You just cut off the flat four plug and reattach the wires to the 7 way.
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TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
Adventures: 51 Nights: 322 Towing Miles 41,200+