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7-Blade Trailer Wiring Confusion

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  • 7-Blade Trailer Wiring Confusion

    CAUTION THERE ARE TWO DIFFERENT STANDARDS! Explanation below.

    Last week I took my 2009 Toy Hauler (basically a travel trailer with a garage) to the Texas Hill Country to ride the three twisted sisters. Shortly after leaving, the trailer controller on my truck (a 2006 Ford 350 Dually/Crewcab King Ranch with an optional in dash factory trailer brake controller) started flashing a Trailer Fault message - and I had no brakes on the trailer. My toy hauler is very heavy (newer ones are far lighter) and since I was riding curvy roads with steep inclines, it was nerve racking and I had to give about three times the normal following distance. I carry a can of CRC Electrical Contact Cleaner in the tool box of the truck, and I stopped and sprayed both sides of the connection heavily, but it didn't help. I did have lights, but no brakes. I looked in the trailers female plug and the aluminum blades were pretty corroded.

    As a side note, the best way to stop this corrosion is to smear a little axle grease (works better than any other grease including Lithium and Dielectric) but I've only had this trailer for two years and it sat on a consignment lot by the Gulf for a couple of years.

    Once home I plugged in a $10 tester I have, and verified my truck wasn't the problem. BTW, one of these testers (got mine on Amazon) are really handy have in your toolbox.


    So my choices were just lop off the plug end and wire a new end on, or spend <$25 and replace the whole 8' cord at the trail's junction box. I choose to replace the whole cord as the plug is molded into the cord - making it weather tight and stronger. It also gave me an opportunity to inspect the connections in the junction box. That was a good thing because the junction box in my case was a small electrical box that contained a spaghetti bowl of wires and wire nuts. Had I known that, I Would have most likely bought a real trailer junction box, which is a weather tight box with a terminal block inside. Wires from trailer are screwed on one side of block with round connectors, and wires from cable on other side of block. If your trailer doesn't have a junction box, spend the couple bucks to do it right. A good place to mount is inside the trailer's A-Frame for tag trailers.


    In my "not so weather tight" box, I had mud dauber nests that I needed to knock out, and I also took the opportunity to trim the ends of trailer wire and strip for clean wire since I was going to have to connect with wire nuts. I took three photos from different angles of wiring, removed the wire nuts, pulled out the old cable, straightened out the rat's nest, and threaded the new cable through the cable clamp. As I started twisting wires together, I found that none of the three black wires showed their source through the rat's nest, and one had to be attached to both blues (to be explained at end), while the other two to the 00 battery cable - along with an orange wire.

    So after scratching my head, I googled for a wiring diagram. It was then I realized that my wires were different then diagram. For instance I had a red wire and the diagram had purple, and the diagram had all of the light wires different. Yellow was for reverse lights on my trailer, but to right turn signal on charts.

    Further investigation had me finding that there are two different standards, which was throwing many for a loop based on questions being asked and not properly answered on google. It turns out that most trailers use the "SAE" standard, However, the Amish use a completely different standard that they refer to as the "Traditional" standard, while others refer to as the RV standard. I have located a chart with both of these standards It will help you to figure out if truck is wired one way and the trailer another - or you get an RV cable instead of a SAE cable. Hopefully, that will save you the time I had to waste researching why I wasnlt wired like all of the charts I was finding..




    So, mentioned that I have an orange wire tied to battery, a black tied to the blues (trailer brakes), and the fact you have to search for hours on what the black coming from the truck does.

    So in addition to the wires from the cable and a mystery orange wire, there are a pair of black and white wires (one each) in a sheath coming into trailer lights junction box. They disappear into the wall and I flat didn't find where they terminate. Now there all kinds of other electrical connections for generator, inverter, charger, 12v lights, fuel pump to refuel toys from generator's gas tank - so this has to be something that the manufacturer felt like should be associated with the tow vehicle. Then again, 30 years of ownership on Amish built motorhomes, boats, and trailers has taught me that the Amish are a little strange about building. They don't need no stinkin plans, and each have their own style. While I don't know what's at the other end of those wires, white is always ground on trailer light wiring (so a no brainer), and it was known that the orange was tied to the battery. That left choosing which of the two remaining black wires was needing to be tied to blues, and which went to battery.

    Further investigation taught me that the black from truck īs a low amp 12v from the truck's battery, hopefully with a diode causing power to only flow to trailer from truck (and not trailer to truck) and something regulating the amps to go through skinny wire. In that way you can charge the trailer's battery while driving. So the black wire from new cable was the one I wired it to 00 cable going to trailer battery.

    That left the black wire kn a sheath with a white wire being the one wired to electric brakes. After much thought, I suspect that must have something to do with the trailer break away applying the trailer brakes, but I never found that to be a fact. Anyway I wired that black to the blue.

    I hooked trailer to truck for a "Smoke Test", and it passed. All lights work properly, and pressing the brakes show the amount of power applied instead of error.

    I hope this helps others who find this thread, because they too need information, but prefer the complete information from one source, and an explanation on the two different standards.
    Maniacal Ravings of an Old Hippie
    Shop Diary of an Old NSS Racer


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