Some time ago I combined and edited/corrected this handy dandy sheet for trailer wiring color codes and positions in all common plugs, as viewed from both front and back of truck and or the trailer connection.

Print it out, laminate it, and keep it with your wiring supplies and tools.

Grigg

ps
It does not have separate picture for flat 4, but they come molded with colored wires. The colors/functions are same as the automotive 6 and 7 wire plugs (not all same as semi truck 7 wire)
Attachments
All 6, revised (J560).JPG (183.46 KB, 134 downloads)

Last edited by Grigg; 10/02/2017 7:56 PM.
•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-