Help with trailer wiring: It works when first wired-up, then stops working

I'm having trouble wiring up the lights on a trailer. I have a 4-way connector, and I believe I've wired it up correctly:

- White to the trailer frame
- Brown to the tail lights
- Yellow to the left turn signal
- Green to the right turn signal

I verified this wiring against the instructions at http://www.therangerstation.com/tech_library/TrailerLights.shtml. Unfortunately, it doesn't work. The tail lights, left turn signal, and right turn signal work when I first wire them up, but not afterward.

To elaborate: If I turn on the left turn signal on the car, then connect the yellow wire, the left turn signal on the trailer works fine, but only until I turn off the turn signal at the car. After that, the left turn signal on the trailer is unresponsive when I turn the turn signal back on. The same is true of the right turn signal and the tail lights -- they work as expected when I first wire them up, but stop working as soon as I turn off the turn signal or lights.

In all cases, I can disconnect the wires and reconnect them exactly as before, and the lamp in question will work properly again... until I turn it off and try to turn it back on. This tells me I haven't burned out a bulb or a fuse. At all times, the car's tail lights and turn signals work exactly as they are supposed to.

I am baffled by this. Does anyone have an explanation for why my trailer lights might work when first wired-up, but then stop working?

Some details: The car is a 1996 Nissan Pathfinder. The wiring harness on the car is an aftermarket T connector which I installed myself (see https://www.carid.com/curt/3-wire-t-connector-mpn-55361.html).

-TC

I would check the continuity of the ground on the vehicle that you used.

"Ditto" Bad ground is most common trailer lighting issues.

Thank you for the suggestions. However, it looks like I have good continuity to the ground. I used an ohmmeter to measure the resistance between the ground of the flat connector and one of the bolts underneath the plastic threshold for the rear hatch (the only place I could find exposed metal). The meter read 0.9Ω. My meter has a continuity test feature which sounds a tone when there is low resistance. Using that feature, there was a strong, continuous tone. If I should be testing the ground wiring some other way, please let me know.

Is it possible that my T-connector is defective? (https://www.carid.com/curt/3-wire-t-connector-mpn-55361.html) The T-connector includes a literal black box that was described as 'a circuit-protected converter'. Might that be 'protecting' the circuit by shutting it down, perhaps in the way a ground fault interrupt does?

Website says it has a one year warranty. I would contact the manufacturer. They may have seen this before.