Only two curcuits working on trailer wiring pigtail

Since I sold my travel trailer, it has been a long time since I towed anything until I rented a skid steer recently. When I hooked the trailer up, I found that the left turn signal and left brake light were thee only things working on the trailer. I didn't know if it was the rental trailer or my plug, but after years of it hanging there exposed to everything Michigan has, I knew the plug might need replacing.

Now that I am picking my new boat up tomorrow, I figured I'd take no chances and put a new pigtail on. I replaced the plug with the same type and wired it the same (obviously).

Using a test light, I see that it WAS my plug that was bad that day, and still is. I only have power to the left turn signal/ brake and reverse lights. No running lights, no right turn signal/brake, no constant power, no electric brakes.

Seeing that the plug is all new with carefully wired connections, I am stumped where to go from here. There is no break in the harness where a "T" connecter could be. The harness just disappears into the chassis and runs... wherever.

By the way, when I last towed my travel trailer over 4 years ago, everything worked.

Any clue for a fella? It is a 2004 GMC Savana 2500 series van.