5 wire flat prong trailer wires into a 4 wire

Thks

 

What a perfect solution. Excellent. Bert

 

Agreed, many are making this a lot more difficult than necessary. It's all about how the car is wired and in most cases, you can use a 5 wire trailer pigtail on a 4 wire car, though the reverse isn't necessary true. Switching the brake/turn for the running as a quick test, which is all it seems this poster needs to do would quickly solve this mystery, without needing to know, how many amps the 12 VDC test bulb needs. It's one thing to understand what's wrong and surmise what's needed, yet another to have actually have done it in the field and made a "cure" in 5 minutes or less.

 

Looking at the photo I see 1 green wire, 1 yellow wire, 2 brown wires, and 1 white wire. Note that the brown wires are next to each other, while there is a space between the other wires. It is a "Flat 4 connector with a wishbone harness", not a Flat 5 connector. The harness has one brown wire for tail/maker paired with the green wire for turn/brake on the right side of the trailer, and one brown wire for tail/marker paired with the yellow for turn/brake on for the left side of the trailer. Link to a vendor's photo of a similar harness.
20 ft. Wishbone 4-Way Trailer Wiring Harness with 30" Ground Wire Optronics Wiring A20WB https://www.etrailer.com/Wiring/Optronics/A20WB.html?feed=npn&gclid=Cj0KCQjw95vPBRDVARIsAKvPd3I0M0htLbDqNXs3pAg8tixLUXIl4YfM0c-cYVdG9OpmJ4EXYAdG4B8aAkrAEALw_wcB

The tow vehicle needs to wired the same as for any trailer with a Flat 4 connector.