Adding surface mount lights to cargo trailer.

Blake

Member
Sep 21, 2016
211
Savannah Georgia
I have a 6x10 cargo trailer that I need to add two surface mount amber lights to. Trailer has standard four way flat connector. To make this oem, will I need to change trailer wiring to 7 way wiring, so that when I activate my truck lights, when hooked up the trailer lights will activate also?
 

801

Member
Jul 14, 2014
679
NV
I added a second 2 conductor wire when I added amber lights to a mounted patrol horse trailer. That way someone wouldn't plug it into a vehicle mistakenly and smoke the system.
 

Shawn L

Member
May 21, 2010
2,477
Corbett, Oregon
we had to do several trailers at work , the problem was that we didn't have dedicated vehicles to tow them, i ended up using all led lights, and put a weather proof switch on the front of the trailer, the lights were wired to the switch, and the switch was wired to the marker light circuit, any vehicle with a flat four connector could tow it and the lights would work, you switched the lights on when you went en-route.
 
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Jarred J.

Lifetime VIP Donor
May 21, 2010
11,580
Shelbyville, TN
solar panel and battery...
 

CEVS

New Member
Jun 1, 2010
264
NJ
If you are going to put the switch on the trailer I would recommend switching to a 7pin plug and utilizing the 12v constant that is in that instead of connecting to the running light circuit.
 
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Steve0625

Member
Jun 23, 2010
1,213
Northville NY

That will work just fine. Those who are familiar with trailer wiring could probably purchase a similar pigtail without the junction box for a lot less money, but what you found will do the job.

7 pin trailer wiring diagrams are all over the net. Easy to find and easy to work with.

The 12vdc constant from the tow vehicle gives you a bunch more current if you wanted to hook up interior lights or additional exterior lights. Check your truck's fuse listings, it will tell you how much amperage that circuit is rated for. If you're going to use all LED fixtures, you'll probably never get anywhere close to the circuit's rating. The constant 12vdc to the 7 way connector is called "trailer tow battery charge" in my '12 F250 and it's fused at 25 amps.

Helpful hint: Some light trucks come through from the factory without the fuse for this line installed. You'll want to check that.
 

Steve0625

Member
Jun 23, 2010
1,213
Northville NY
My Trailer package utilizes a 30Amp Maxi Fuse

OK, just understand that's setup for 30 amp surge and not a constant draw. Light truck wiring is just like automotive wiring; it is not meant to pull comparatively large current draws. I think you'd be OK if you kept the total draw at anyone time on that circuit to about half the fuse rating. But that still gives you plenty of current for several more blinkies than you're currently planning.
 

Shawn L

Member
May 21, 2010
2,477
Corbett, Oregon
to clarify on my suggestion, in our case we were working with smaller single axle trailer that could be pulled by a small suv or even a ranger pickup, if you have a larger trailer or its going to be really loaded down with equipment then going with the 7 way option is a better choice, our trailer were loaded withh spill absorbent pads and containment booms , you could have towed these trailers with a Toyota Camry, we wanted to not limit what volunteers could tow the trailers.

if its a big or heavy trailer maybe you do want to limit who tows it, generally speaking the smaller vehicles are not generally equipped with a 7 way.
 

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