Just got a 92 Coleman popup and trying to get the lights working.
There are no brakes on the trailer, so all I need is the lights
working.  My 4-way on the tow vehicle works just fine on my other
trailers with 4-way connectors, but the new trailer has a 7-way
connector.

I have an adapter and from what I can tell, all is wired correctly,
common ground white on the 7-way to the white on the 4-way,
red on 7-way to yellow on 4-way,
brown on 7-way to green on 4-way, and
green on 7-way to brown on 4-way.

The wiring on the trailer is stock, ground wire connected to each
fixture, fixture themselves not attached to frame.  I added another
ground wire connected to the trailer chasis and then connected to the
ground stud on the trailer 7-way connector.

Problem right now is when headlights are on, running lights on trailer
are on like they should be, when blinker is on all lights flash does
not matter whether right or left.  When brake pedal is pressed, all
lights go off on the trailer.

With headlights not on and either turn signal on, turn signals on
trailer work fine, but  when brake is pressed, all lights flash.

Frustrating!  Not sure what/how exactly to test.  As I said before,
connection from the tow vehicle works perfectly with my other two
trailers with 4-way connectors. Acutally hauled one out to make sure i
wasn't loosing my mind.

To test, connect the negative of a battery to the frame and then touch
each lead on the trailer connector?