Pulling my hair out--4-Pin trailer wiring

[Cyn]

I have a partial pop-up camper trailer--just the frame and bottom remain (also tires, hitch tongue, etc-it pulls fine).

I'm trying to get it ready to register and use, but have run into wiring problems.  I got a brand new OEM compatible wiring harness for my van, and it was easy to attach, the ends plugged into the matching parts inside the taillights, all color coded and labeled. I plugged in the wiring from the trailer, both are 4-pin connecters, also color coded, yellow brown, green, white, and each wire says on it where it's usupposed to go, so I wired everything after researching and comparing several different but identical guides from the packaging and internet pictures. 

With the engine running:

The taillights come on when I turn on the headlights. Fine, ok.

The turn signals both come on when I turn them on in the van, both flash whether I'm doing left or right.

When I push the brakes, the taillights both go out, returning when I let off the brakes.

I only have the yellow wire on the left side, and the green wire on the right, matching directly the ones coming from the van, and each light fixtures. The brown wire splits and goes to both brown wires in the right and left fixtures, too.

I had several splices before to lengthen the wires to fit, but today I replaced that with all new wires and minimized the superfluous connections to no avail, everything still does what it wants to regardless of which switches I use.

I haven't even tried to add the marker lights into the mix, yet.

What can it be??

[Lakota Wolf]

Just a thought,,, possibly a reversed PARK/Running Light and Brake light.
I should ask,, When park lights are on,, Are the trailer lights normal dim (light a running light) or Bright,(as if the Brake light is on )? This is NOT even pushing the brake pedal, Now on to suspiciaon number 2 , Are your trailer lights on a COMMON WHITE ground? And is the White grounded to the trailer AND the plug?

I bring these to common problems up because the original grounds (white) on the trailer where corroded,, and the white wire on the pigtail plug in (white) was also corroded where it attached to the trailer..
I always carry those magnetic lights from Harbor freight for testing the pig tail off the vehicle to make sure the wiring to the plug was correct if I came across an issue (s) as you are having.. So called my $10 trailer Test light kit.

[Russell E Johnson]

What Lakota said. From the various wiring problems I have fought I would start by making sure all the ground connections are good and that the trailer and tow vehicle are hooked together with a ground wire.

[Cyn]

Thanks Lakota and Russ, I'll be looking at the white wires tomorrow.  That may be the problem.

[John "T" Nordhoff]

 I can't say not being there, but OFTEN on the older 3 wire systems, the White is frame Ground,,,,,,,,,,,,,,Green is Right Turn & Stop,,,,,,,Yellow is Left Turn & Stop,,,,,,,,,,Brown is Tail/Marker.

 So many trailer .light problems are due to a bad ground connection

 John T

[Cyn]

PROBLEM SOLVED!! :) "So many trailer .light problems are due to a bad ground connection"--yes indeed!

The ground wire was disconnected between the 4-pin thingy on the trailer side, to the rest of it's wire--duh! moment.  Everything does what it's supposed to now, so now I'm hooking up the markers and all will be finally ready to go!!

Thanks so much for all the help!

[Russell E Johnson]

I am so glad to hear that the problem is solved.  You did good.