7 pin cable

[marpel]

Due to a bit of age/corrosion, I have decided to replace the 7 pin plug/cable on the trailer.

As I usually do when I am about to tackle something I haven't previously dealt with, I searched the net and YouTube for tutorials/instructions just to make sure I don't miss anything.

The funny thing was, out of all the vids/articles I reviewed, only one could be found that touched on replacing the entire cable (ie wiring directly into the junction box).

Every other one described how to either replace the plug (by cutting the old plug off) or cutting/splicing the cable farther up. In fact, in one video, the fellow showed the old cable, and existing junction box, then proceeded to cut the old cable halfway, and splice in a few feet of the new cable and plug using another junction box to connect the new and old cables, then fastening the new junction box right next to the existing junction box (with the old cable running from one box to the other).

To me it seems simpler to remove the entire old cable, get a new cable and run it right to the existing junction box. Or am I missing something??

Marv

[MEXICOWANDERER]

If I may inject a tip here regarding smaller insulated wire terminals.

When choosing the type of wire terminals to buy, you might want to specify NYLON insulation over PLASTIC

Wire size terminals are color coded

Red for 18 gauge
Blue for 16-14 gauge
Yellow For 12-10 gauge

Nylon insulation is tinted like red, blue, and yellow but unlike plastic you can see the barrel of the terminal. It is translucent. Plastic is opaque.

Why Nylon? Nylon insulation is a lot tougher than plastic. This allows me to choose a different much tighter crimp without puncturing the insulation.

Most crimpers give a () shaped crimp. Keep searching on Amazon or eBay and you'll stumble upon a () plier that has a < on one side. The tip makes all the difference.

I've won bets from people who claim the tip shape of the crimp will hurt the nylon. It can't. But it squeezes the terminal much tighter onto the wire.

I have not tried this with terminals that have heat shrink ready to go, so I urge caution. In fact with heat shrink terminals or solder shrink terminals I would urge checking into a vice grip type of crimping pliers.

[marpel]

Thanks for the continued replies/advice.

The question about the 7 pin cable came up prior to discovering an issue with the brakes (other thread), so Grit dog is right, I suppose I need to figure out the brake issue (which may be related to the cable, I guess).

Marv

[Grit_dog]

But none of this matters until you diagnose your brake problem.

[Grit_dog]

OP, know that there are 2 different wiring/color conventions for 7 pin trailer hookups.
I wasn’t aware of this until I bought a pre-wired plug and pigtail. It and others since then are all wired to a different color convention than I or most are accustomed to I believe.

And I didn’t say anything g about wire nuts in this thread I believe, but yes I would consider using them in a weather protected J box.

[Vintage465]

Yes, the 7 pin with brass terminals in the plug and J-box at the other end is the ticket for me. I installed one on my sis's right and it worked out great. And as mentioned above, crimp connections with the integrated heat shrink on the existing wiring to get it into the new J-box just about eliminates any chance of connection failure when done correctly.
https://www.etrailer.com/Trailer-Wiring/etrailer/e99011.html?feed=npn&utm_source=google&utm_medium=cpc&utm_campaign=Google%20%7C%20Shop%20-%20Trailer%20Wiring&adgroupid=128484934262&campaignid=15586143335&creative=569877447301&device=c&devicemodel=&feeditemid=&keyword=&loc_interest_ms=&loc_physical_ms=9052718&matchtype=&network=g&placement=&position=&gclid=CjwKCAjws8yUBhA1EiwAi_tpEeDOl6XW5mY39SSDuW59vULY4aYi9LfKehQvmijD5uTThuMQ0M_oexoCarcQAvD_BwE

[Gdetrailer]

Dusty R wrote:


True, but I do have the proper tool. I'm a retired construction electrician. And if I remember right, a box is required when the voltage is above 35 volts. On a trailer a box collects road salt and rusts.

I have worked in consumer and industrial electronic repair jobs for more yrs that I wish to count and also have wired from scratch a few homes including my own so I am well versed in having and using the proper tools. Many of those tools are far more expensive than the average home owner would want to spend on for casual repairs.

It is easy to forget that many times folks gravitate to grabbing pliers and smashing the heck out of a crimp splice either because they do not understand how to make a good crimp that lasts or have the tools but take a short cut with pliers..

[Gdetrailer]

marpel wrote:
Thanks for all the replies:

Just to clarify though, the new cable was not too short as the new box was placed right beside the old box, so the, loosely strung, replacement cable appeared able to reach the old box quite easily.

And BB_TX, your description was exactly what I was planning on doing. Take photos or label current box layout and just repeat with new cable. Logically seemed pretty straightforward.

Just figured, because no-one seemed to want to tackle the junction box connection in any of the vids/tutes, that I was missing something that made it difficult.

Marv

Guy in the video was a bone head and taking the lazy way by not dealing with the wires in the original junction box. Basically a "cut and match color" approach.

The cable has a wire color code, the wires from the trailer body terminating in the original junction box will not have the same color coding. This presents a problem if you just remove all wire nuts and wires at the same time (which the bone head in the video most likely would have done).

The simple and easy way to change the cable without losing track of the correct color coding is to cut the wires from the cable you are replacing, leaving an inch or so of the old wire with the color showing. Now you can remove the old cable, insert the new cable and one by one match the new cable wire colors doing one connection at a time..

This method works well but I have run into a couple of cables that had some non standard colors or wiring of the plug.. Check and verify the positions on the plug with the wire color. A Digital Volt Meter (DVM) set to OHMs will allow you to check and verify each position without needing to plug cable into vehicle.

I actually bought an extra 7 pin socket that would be mounted to a vehicle and ran wires out of it and labeled each wire as to the function. Then I made a cable with a fuse and gator clips on each end to connect a small 12V battery to test trailer plugs before connecting to my vehicles..

Just towed a 35ft park model for my FIL recently, was able to use my test socket to verify the 7 pin cable was indeed wired correctly before committing my vehicle to that unknown plug..

[BurbMan]

I just replaced the cord on my 5er for the same reasons. My initial thought was just to replace the plug, but since the plug is out in the weather, I would rather have a molded connection there, so I replaced the whole cord.

First measure your existing cord and get one the the same length. I got this cord from Amazon that comes in 8', 12', and 16' lengths. If your size is in between you can always shorten the cord.

The cord typically terminates in a standard 4" steel j-box. On my 5er, the box is under the pin box, and even though it's open to the elements on the bottom, it's well enough protected that the screws on the cover and cable clamp weren't rusted to death.

On my TT, the box was on the frame up under the Coroplast underbelly material, keeping it dry and protected from the elements.

It makes zero sense to add a second j-box on this cord unless the factory put the original j-box in a location that is impossible to get to. Otherwise, it's just a matter of opening the box, matching the colors, and connecting the new cord. Pay attention to the colors used on the trailer side and also how the breakaway switch is wired in. As you know in residential wiring black is hot and white is neutral, and in auto wiring red is hot and black is ground. Some trailer mfrs follow the black/white convention for 12v wiring, some follow the black/red, so pay attention to how yours is wired.

Typical 7-pin cord will have 2 #10 black/white wires for (+) and (-) charging lines, a #12 blue wire for the brakes, and 4 #16 wires for the lights. As Grit Dog says, the factory uses wire nuts and they work just fine.

[Dusty_R]

Gdetrailer wrote:

Dusty R wrote:
I would use crimp butt splicers and Heat Shrink insulation tubbing.

:R

Rookie mistake.

Crimps work best with proper quality crimping tool, very few people have the proper crimping tool and substitute pliers and crush the connection making a very poor and unreliable connection.

Additionally, standard heatshrink tubing is not weather proof or water tight and moisture will destroy the connections hidden inside the tubing.

Not to mention the average backyard electrician won't have a good heat gun and will use matches or a lighter to shrink the tubing making a mess of the job..

For heatshrink tubing to work in the outdoors you must get adheasive lined tubing, it has a heat activated glue that surrounds and seals around the wire insulation making a good water and weather tight seal..

But, a good electrician will try to avoid allowing connections to be exposed to weather which means taking the connections back to the original connection box which is protected from the weather.

Inside that box, the connections are made with wire nuts, no need to reinvent the wheel. Just use the existing wire nuts inside that box and all will be fine.

True, but I do have the proper tool. I'm a retired construction electrician. And if I remember right, a box is required when the voltage is above 35 volts. On a trailer a box collects road salt and rusts.

[Grit_dog]

No, you’re tracking right. Replace the cable back to the j box if you need to.
If no issue with the cable though, no reason to not just replace the plug if it has issues or serious corrosion.

Fwiw, I’ve not had good luck with the pre-wired molded Plug pigtails. Have another one I installed a couple years ago that is shorting out somewhere in the molded together plug.

[marpel]

Thanks for all the replies:

Just to clarify though, the new cable was not too short as the new box was placed right beside the old box, so the, loosely strung, replacement cable appeared able to reach the old box quite easily.

And BB_TX, your description was exactly what I was planning on doing. Take photos or label current box layout and just repeat with new cable. Logically seemed pretty straightforward.

Just figured, because no-one seemed to want to tackle the junction box connection in any of the vids/tutes, that I was missing something that made it difficult.

Marv

[Gdetrailer]

Dusty R wrote:
I would use crimp butt splicers and Heat Shrink insulation tubbing.

:R

Rookie mistake.

Crimps work best with proper quality crimping tool, very few people have the proper crimping tool and substitute pliers and crush the connection making a very poor and unreliable connection.

Additionally, standard heatshrink tubing is not weather proof or water tight and moisture will destroy the connections hidden inside the tubing.

Not to mention the average backyard electrician won't have a good heat gun and will use matches or a lighter to shrink the tubing making a mess of the job..

For heatshrink tubing to work in the outdoors you must get adheasive lined tubing, it has a heat activated glue that surrounds and seals around the wire insulation making a good water and weather tight seal..

But, a good electrician will try to avoid allowing connections to be exposed to weather which means taking the connections back to the original connection box which is protected from the weather.

Inside that box, the connections are made with wire nuts, no need to reinvent the wheel. Just use the existing wire nuts inside that box and all will be fine.

[Dusty_R]

I would use crimp butt splicers and Heat Shrink insulation tubbing.

[Gdetrailer]

Fisherman wrote:
Maybe the new cable was too short for his application. More contacts and breaks, more corrosion possibilities and breakdowns. I would go with one junction box.

X2!

Most likely the person in the video was not able to get a cable long enough so splicing somewhere else would be needed.

Not ideal but could work in a pinch.

As someone else mentioned, they do sell prewired/molded cables with plugs in different lengths and even different wire ga sizes. You can also buy bulk wire for 7 pin harness to customize your cable to the length you need and then add a replacement plug to that.

Much better however to get a cable long enough or even a bit longer in the first place and go back into the original junction block. Otherwise you are adding an additional point of failure with an additional splice.

Extra junctions or splices can eventually come back to bite you in the behind and that typically happens at the worst possible time..