Why do both my boat trailer lights blink when I turn on the running lights?

Boat trailer lights both blinking when I turn on the running lights on my Nissan truck. I have ok signal from the light converter box. I have replaced both tailight units. Strange things is when I plug into our van all the trailer lights then work?

How do I check all the grounds? I am ready to go have it fixed...

Any advice, or help will greatly be appreciated....thanksWhy do both my boat trailer lights blink when I turn on the running lights?
It's not the ground, it's the hot wires that are not in sync. The plug on your car wired wrong.Why do both my boat trailer lights blink when I turn on the running lights?
On Japanese brand vehicles you need to get a converter wiring box. The Japanese vehicle's brake and tail lights are wired differently than other vehicles. I've seen them for sell in WalMart and U-Haul. Part stores would probably have them as well. Or you could get them online.

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