Typical trailer light function has a single filament for brake and turn, to signal a turn it interrupts the left or right brake light on the trailer. (running light is another filament for that only)
Your truck might not be wired in this way, you may have a stand alone brake light, and a stand alone turn signal filament? If so and without the right turn signal unit then your trailer wiring gets confusing.

A Signal Stat 900 turn signal switch is in my opinion the best aftermarket option, choose the 7 wire version and not the 4 wire. With the 7 wire it's real easy to power a trailer light plug properly. You can also have separate turn only bulbs on the truck if desired.
http://www.truck-lite.com/webapp/wc...;productId=47726&urlRequestType=Base
Not this
http://www.truck-lite.com/webapp/wc...e=Base&langId=-1&catalogId=10002

I suggest using the standard color code and positions for the standard trailer plug of your choice.
It's real frustrating having to rewire your trailer or truck to work with someone else's truck or trailer because you have something non standard.


•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-