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How to Add 7-Way Wiring to Rear of Flagstaff 5th Wheel to Allow Towing Boat Trailer


I am wondering where to attach a 4 pin flat plug at the back of my Flagstaff 8528IKWS, I will occasionally be pulling a boat trailer and need to have it wired forrunning, brake, and signal lights. Some run them right from the front of the trailer but others say you can tie into existing wiring at the tail lights at the back of the trailer. I was hoping you could assist with this or provide a wiring diagram. Thanks.


Expert Reply:

The 4-pole format of trailer wiring includes only basic lighting signals for stop, tail and turn lights; in order to have trailer brake power you will need to convert the wiring to at least a 5-pole (one more circuit for brakes) or to the popular 7-way format which has circuits for brakes, reverse lights and auxiliary 12V power. An article on wiring is linked for you and this includes details about the circuits found on each type of wiring format.

If the taillight wiring in your Flagstaff 5th wheel is heavy enough to handle the extra power drawn by the lights on the boat trailer you wish to connect then you can tap into that wiring to get the basic lighting signals. I suggest checking with Forest River using the trailer's VIN. They can tell you if this is safe or if you need to run new wiring from the front of the trailer to the back.

The most secure way to add the new wiring is to install a junction box # 38656 on the front of the trailer which can serve as the connection point for both the existing wiring and the new 7-way wire # DW04914-1 you will run to the back of the trailer. You will need ring terminals like # 44-5310A. This can then connect to a 7-way socket like # HM48480.

Please note that tandem towing (towing two trailers at once) may not be permitted in all areas so you might want to check this ahead of your next trip.

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