Best plan of attack for 4 & 7 pin wiring? - Fiberglass RV


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Old 06-08-2014, 04:32 PM   #1
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Best plan of attack for 4 & 7 pin wiring?

I'm visiting the in-laws while in Chicago on business. We drove from Colorado so we could finally get around to inheriting "The Egg" ('72 Boler).

I'm getting it ready to tow home & first thing was the 4 ping plug was chewed or torn off. A quick look indicates that the missing 4 pin flat connector probably wasn't original (any guesses what the original plug was?) . I tested out the wiring with 12v & got life on the side markers, but nothing on the rear running lights or turn signals. Rather than troubleshoot crusty old wiring I'll just run new, it will be cleaner, safer & probably even faster.

My Tacoma has a 7 pin connector & the wife's Escape (what we have here in Chicago now to pull it home) has the 4 pin flat. Ideally I'd like to set it up to support both. I have a 7 pin to 4 pin adapter for my truck, but haven't really seen anything to take a 7 pin trailer plug to connect to a 4 pin tug connector on Amazon or Etrailer.

At the moment the trailer doesn't have a battery, but I'm planning on adding one & generally fitting it out for boondocking. The 4 pin will work for now, but ideally I'd like to set it up with both so it can be towed by whatever, but will charge up the battery on the trailer if the tug can supply power.

For now I'll probably just wire it up with a 4 pin wiring plug/kit we have on hand & will get us down the road with the Escape. However i am thinking I'll cut that & wire in a breakout box next to the hitch down the road so I can do something fancier down the road. Any suggestions on how to optimize things for both 4 & 7 pin connections?

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Old 06-08-2014, 05:13 PM   #2
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For the Escape, Hopkins makes a combo 7 and 4 pin that the 4 pin from the vehicle plugs into. Then you simply run power and/or brake lines for full functionality.
Multi-Tow® 4 Wire Flat to 7 RV Blade & 4 Wire Flat
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Old 06-08-2014, 06:00 PM   #3
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There is a standard accessory 7 pin connector at the RV store that has a 4 pin pigtail on it and three leads for the brakes, charging line and accessory pin. You just plug the pigtail into your existing 4 pin TV lead and wire up the others as needed or not needed.

I have also seen the same type of connector with both a 7 pin socket and a 4 pin socket on the same molded mount.
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Old 06-09-2014, 12:28 AM   #4
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I replaced the TV connector on my dually recently. One of the six spades on the outside broke off. I like my new one better-- it provides connections for both seven pin and four pin flat, but not at the same time. I would have liked to be able to use both as I have been hooking my pickup camper to the trailer connector and have several small trailers w/ 4 pin flat, I might want to pull at the same time.

I have the parts to repair the in bed connector but I can't get at it with the camper mounted in the bed. And I'm not sure I'd want to jack up the truck camper if I had a problem.

These offer the advantage of not needing an adapter and also the capability of pulling power for something else with the second connector although that might mean breaking off the door such that both would fit at once.
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Old 06-09-2014, 07:21 AM   #5
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For my towing fix I went to Harbor Freight and bought the cheap towing light kit and stay strapped it on the back of the trailer and some duck tape on the sides to hold the wiring up. That worked like a charm and then when I got home I was able to dig into the wiring and fix it correctly.
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Old 06-09-2014, 09:19 AM   #6
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I got my Scamp home with a set of magnetic trailer lights from HF. It took an extension I had thought ahead to buy from the place that wired my 7 pin plug & brakes on the truck. I have seen those combo 7 & 4 pin TV plugs and would go that way if my TV was not already wired for one or the other. All that said, my advice is to just wire your "new" trailer for 4 pin and set yourself up with solar for boondocking. From what I have read you don't get a complete charge on the trailer battery from the TV anyway. Something to do with small charging wires running back, tug & trailer battery mismatch, etc. Maybe buy a small 120v battery charger for a good charge at home and if you are camping where they have hookups.
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Old 06-09-2014, 09:33 AM   #7
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I would always opt for going with the 7 pin connector, here's why:

1. The plugs and receptacles are sturdier. The usual 7 wire lead is almost indestructible.
2. You always get some free charging time when you are driving and, if needed, you can top up the battery at a campground with the TV should it be needed (even at night)
3. Solar is an additional expense and still isn't an all inclusive solution for everyone.
4. It's another option to assure a good camping experience, and it's very inexpensive to do..
5. There are lots of adapter plugs/cords to go from 7 pin on the TV to almost anything under the sun
6. Emergency Jump Battery: I have actually used the coach battery to get enough life back into the engine battery to start it when it went dead overnight. (Plug in the 7 pin connector, bypass the isolator if you have one, wait about 30 minutes and off you go!)

Good Luck
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Old 06-09-2014, 09:48 AM   #8
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For my two cents is you need that extra wire for electric brakes.

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Old 06-09-2014, 10:03 AM   #9
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I didn't mention that because it didn't appear that this 42 y.o. Boler ever had brakes, but that's a good plus for the future.
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Old 06-09-2014, 10:22 AM   #10
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Originally Posted by Bob Miller View Post
I would always opt for going with the 7 pin connector, here's why:

1. The plugs and receptacles are sturdier. The usual 7 wire lead is almost indestructible. And more expensive, and bulkier for an application where it is maybe not needed. I have never had a 4 pin "fail" for lack of "sturdiness".
2. You always get some free charging time when you are driving and, if needed, you can top up the battery at a campground with the TV should it be needed (even at night). Running your TV to charge the trailer battery is the most inefficient mode possible, and would be better done with the TV turned around and running large gauge jumper cables if it is that important.
3. Solar is an additional expense and still isn't an all inclusive solution for everyone. The OP mentioned boondocking and solar is a natural solution they might as well start investigating. Per the OP: "At the moment the trailer doesn't have a battery, but I'm planning on adding one & generally fitting it out for boondocking."
4. It's another option to assure a good camping experience, and it's very inexpensive to do. I don't know how much of "good camping experience" a 7-Pin provides, but true the labor in pretty much the same either way.
5. There are lots of adapter plugs/cords to go from 7 pin on the TV to almost anything under the sun. True, but his TV (the Escape) is not currently wired for 7 pin.
6. Emergency Jump Battery: I have actually used the coach battery to get enough life back into the engine battery to start it when it went dead overnight. (Plug in the 7 pin connector, bypass the isolator if you have one, wait about 30 minutes and off you go!). As with the note on charging above, turn the rig around and use your jumper cables and go now, not (maybe) 30 minutes from now if you can bypass something to make it work.
Good Luck
I just don't see the point having to re-wire the Escape (or buy an adaptor) just so you can use the 7 pin now. Don't let perfect get in the way of good enough.
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Old 06-09-2014, 10:45 AM   #11
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You can get adapters that go both ways. I got one of these for my Scamp and it works great.

But be advised... the connector I got wasn't grounded properly. The ground wire coming from the flat 4 connector was not being passed through to the ground pin on the 7-blade connector because they expect you to ground it to the vehicle. If you have this problem, just connect the white wire from the flat 4 connector to the white wire that's sticking out of the harness and everything will work.

And if all you need are lights, you can safely ignore the other wires. They are for the back-up lights, 12V power, and electric brakes.

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Old 06-09-2014, 12:19 PM   #12
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The above pic is exactly what I too use. You can plug in your existing 4 pin to the pigtail and go. The additional wires can be added later, there is no "rewiring" needed. And to respond to Post #10

1. In my experiences I have seen a number of 4 pin connectors fail, they seem to loose their ground wire first. I always recommend replacing them with a 7 pin even if it's not needed.

2. Ya better tell all of the other trailer peeps with charging lines that they are wasting their time, not to mention all of the motorhomes out there that charge their coach battery in the same manner. It's worked for for me for over 40 years.... the most inefficient way to charge a battery is to not charge it at all.

3. I almost never park where there are hook-ups (Boondocking?) and have traveled for weeks at a time without any battery problems. Again, a charging line is cheap, quick and offers a lot. Solar involves additional expenses and installation.

4. Having a charged battery as well as some back up options contribute to a "good camping experience" especially for those new to the FGRV world. Having a solar system in no way obsoletes the need for a charging line.

5. See my first comment, it is already wired to plug into the 7 pin connector shown.

6. When you have a dead TV battery it can be somewhat difficult to move either the TV or the trailer to get the two batteries within reach of each other. Add to that, some coach batteries, such as on my Hunter, are located inside the coach.

Much of the time when parking for overnight stays we don't even unhitch. Of course one could always remove the battery from the FGRV and move it to the vehicle, but what I was saying was just an added advantage to having a 7 pin connector/charging line

And so far, I haven't heard a single negative reason other than it will cost a few dollars to gain all these advantages, but much less than adding solar for the first trips out.

Some peeps wear belts, some wear suspenders, some both. If you are new to wearing pants, both isn't a bad idea at all.
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Old 06-09-2014, 12:21 PM   #13
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It was about $45 or $50 to get our Escape wired for 7 pin (without brakes being installed) at local U-Haul store. Have a 7 pin to 4 pin adapter plug.

Trailer is designed to have a 7 pin plug so I would install that on the trailer. Especially if I was having to re-do the wiring. Wire it stock and standard would be my choice.

There is a reason the pre-built 7 pin TV to 4 pin trailer adapter modules are common and all the 7 pin trailer to 4 pin TV adapters have all those extra wires, that reason is safety. IF the trailer is 7 pin it may have brakes, bypassing those is a liability so they manufacture the 4 pin to 7 pin with the wires leaving you with the liability.

A nice heavy 8 gage power wire and battery isolator is a pretty well established way to keep the RV battery charged, nothing exotic about that set up and that is easily done using a 7 pin plug. Some people even add a yellow fog light to the back bumper of the trailer connected to backup lights of TV. 7 pin allows for that accessory, and it seems as if that would be handy backing into a spot after dark.

Saw a post recently where the solar plugged into the 7 pin to charge the RV battery when parked. Using the two connections that TV would use to charge battery on the road. Think that was a portable solar panel, not mounted and hard wired.

If the TV has a hitch adding a 7 pin plug and wires certainly won't hurt the value in terms of resale. Having a stock 7 pin plug on the trailer likewise adds value.

I think the value of features and resale is greater for getting everything on 7 pin than it is for rigging a custom adapter set up to avoid putting a 7 pin on one TV. Will say I have been known to cobble something together that will work so not going to slam anyone that wants to suggest OP go that route.

PS by cobble I mean no disrespect, git-r-done is sometimes appropriate.
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Old 06-09-2014, 11:03 PM   #14
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After digging further & finding multiple wires twisted together (not even wire nuts, which are still bad for a mobile application) I just decided to rip everything out. I'm 7' of brown wire & tightening down a few nuts short of testing it all out & buttoning it up with a brand new 4 pin wiring harness. As I said, for today there is no battery so 7 pin is moot.

Once I get it home & do up the rest of the electrics, there will be a battery to deal with. Looking at the suspension, there is about 1/2" between the axle arms & the frame while it's got the feet down. I'm assuming it's going to end up needing a new axle to replace the presumably 40 year old rubber in the original one. I suspect I'll be thinking heavily about getting one with brakes, which would necessitate a 7 pin at that point.

I was hoping to keep it universal with a 7 pin & 4 pin, so whoever borrowed it, or whatever vehicle we happened to have could pull it, but I'm starting to think 7 pin is the way to go. Retrofitting a 7 pin to the Escape should be pretty easy. When it comes time to go to the 7 pin, I'm planning on just cutting the harness up front & putting a junction box in, to make further modifications & breaking out power/brakes from trailer lights easy.

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