Everything on the newer truck is controlled by computers, not common sense. First look at the truck's rear lights to see if the brake light and the turn signal use the same bulb. Most newer vehicles use a separate bulb for each function. That makes the turn signal switch much less complicated and less costly, but it sure adds a pile of aggravation for trailer owners. At first you were required to buy an adapter harness from the dealer to run the standard lights on trailers, but in the last five to ten years, lighting relays have been built into the under-hood fuse box. Look for a "trailer tow", "trailer brake light" or similar relay sockets where the relays are missing. If you bought the truck with an optional "trailer tow" package, those relays should be there already. My 2014 Ram came with them installed from the factory.
If those relays are missing, you will need to install them, but almost for sure the trailer lights still will not work. If so, you will need to bring your wallet to the dealership and have them install the software to teach the computer to run those relays. That is one of numerous customer-unfriendly business practices GM has pioneered to separate you from your money after the sale.
If we need to dig into this further, let me know if you have a separate left rear brake light and signal light, or if one bulb does both functions. Tell me too if you find those relays under the hood.
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Saturday, December 16th, 2017 AT 10:48 PM