Welcome to the forum
Trailer brakes are electrical, and there is two different ways to activate them. Either using the brake controller or by activating the break-a-way switch. The break-a-way is mounted to the front of the trailer and in your case probably the pin box.
Just like your previous trailer, it will have a plastic plunger inserted into a slot and a cable attached. If it's not fully inserted or missing the brakes will receive full voltage and lock up. UNHOOK the 7way cord and check your brakes. If your brakes are still locked, the issue is with the break-a-way. If brakes are off, you have a wiring issue.
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.