I searched here and could not locate a definitive answer. Am I missing something, connecting to the GX's trailer wiring harness? Whether I connect to the 4-flat or 7-round connectors, I get the same results: tail lights but no stop or turn signals. And to eliminate any trailer wiring issues, I used a test light.



Tail/running lights

Left turn signal

Right turn signal



Helpful owner's manual

Can anyone provide me some insight here???

 

This trailer circuit is absent from any electronic FSM I have.. I do have a '12 official physical Lexus wiring diagram book that may help shed some light if you find that fuses are all in order in engine by and under dash

I'll try to scan tomorrow but it is like 700 page book so takes some time via flatbed scanning

 

Is the 4 plug connection & connector factory? it does not look like mine at all. On mine there is a round multi-connector that plugs into the back of the combination 7 & 4 connector factory trailer connector. If the extension wire shown is an aftermarket item I would be checking it for continuity and checking the factory harness under the back. Could just be a bad aftermarket harness.

 

Good point... MarkVII: Are you plugging directly into OEM



Looks like extension off of something else

 

Extensions plugged into the OEM connector. Test light used directly into OEM connector with the same results- 12v +, tail lights only.

 

This reference identifies a number of fuses labeled "Towing" in both the under dash and under hood fuse boxes.
https://fusecheck.com/lexus/lexus-gx...3-fuse-diagram
Worth a quick check.

 

Thanks!! Both fuses good to go.

 

Direct to OEM connection

 

It shows 8 fuses for "Towing"
#4 & #39 Passenger compartment fuse box
#11, #22, #27, #45, #46, #60 Engine compartment fuse box
Best to always eliminate the simple and obvious before more complex diagnosis

 

Guess I read far too fast or it's time for an eye exam

 

LOL, I can relate, I'm old and cannot see anything without reading glasses.

 

Now, I can safely say , all eight have been checked good, with a volt/ohm meter. . . thanks again!!

 

Not sure if you still needed this or not

 

I certainly do. Thanks!! This looks like it's going to be a project.

 

This is a long shot but you are using the harness ground for testing the circuits. Just for curiosity sake use the chassis for a ground to test both the light circuits and the ground. Although not is this scenario but I have seen a feedback loop where the ground becomes hot. Just an easy diagnostic step and will help narrow the problem