Junction box wiring help

CharlieRN

I'm in the process of installing a DC-DC charger and would like to disconnect the lead on the 7-pole harness that connects the chassis battery to the house battery. This is a bit more complicated in my case as I have a Prodigy RF controller, so have more wires in the junction box. The dealer did the install before I picked the trailer up, so this is the first time I've opened the junction box.

I will of course check continuity from the 12v power pin on the harness plug to the wire in the junction box, but thought I'd try to narrow things down a bit if possible. It looks to me like the 12v connection is the black wire attached to the last stud in photo below. Does anyone know if that's correct?

Bayliss

@CharlieRN, take a look at the Electrical Resources folder:

https://tab-rv.vanillacommunity.com/discussion/6406/electrical-resources#latest

I prepared a diagram of the junction box (J-box) for my 2019 320 S (at the bottom of that folder), which may be of assistance.  It is likely wired the same as yours, but I can't say for sure since the dealer may have changed something.  However, if you view the terminals as #1 through #7, left to right, the black wire going to terminal #1 may actually be from the trailer brake(s) connection.  The 12V connections should be to terminal #6 (red wires), with the ground wires connected to #7 (white wires.)

My belief is that the blue wire stretching along the top of the J-box, connected to terminal #1 is coming from the tow vehicle brake connection, but I can't say for sure since mine enters from the lower right, whereas yours enters from the upper right.  Also, I'm not sure of the source of the orange wire connected to terminal #6.  Your photo is a bit confusing to me, because the entry points for the wires are located different from mine.  Also, the ground connection to the trailer frame, as depicted in your photo, is on the opposite (right) side of the J-box as compared to mine (which is on the frame to the left of my J-box.)  It almost looks like your photo is flipped upside down, but it must not be since the terminal connections appear to be the same as mine (from left to right), for the most part.

NOTE:  Your J-box appears to be mounted at a slightly different location than mine.  Mine is mounted to the frame below the front of the trailer body.  When I am facing and looking directly at my J-box from under the trailer A-frame, I am viewing it looking back in the direction of the rear of the trailer.  I may be mistaken, but yours appears to be mounted on the side of the A-frame.  Just curious about that.

Denny16

You do know, Hse disconnecting the 7-pin TV battery + lead, will disconnect your Prodigy RF controller from getting the 12VDC it needs to work?
 Cheers 

Sharon_is_SAM

Interesting - our Prodigy RF brake controller basically plugged into the TV and the TaB 7 pin - no alteration of the wiring in the junction box.  

Denny16

Good point Sharon, I was also wondering why they had hard wired the controller.
 Cheers 

CharlieRN

Denny16 said:

You do know, Hse disconnecting the 7-pin TV battery + lead, will disconnect your Prodigy RF controller from getting the 12VDC it needs to work?
 Cheers 

While I didn't consider this aspect of the modification before reading the reply, I'm disconnecting the 12v wire at the junction box, which is downstream from its connection to the Prodigy. I'd think that the operation of the RF controller wouldn't be affected.

It's a bit hard to read the label of the box in the photo below, but it's the Prodigy, which is wired into the harness. The plug of the harness mates to the 7-pole receptacle on the TV which has the live 12v pin. The connection from the TV to the Prodigy remains as before, so it should get power.

Is my thought process on this faulty? 

 

CharlieRN

Thanks for the link to the resources folder @Bayliss, and for your comments as well. I did a quick search for "junction box" prior to the original post, and got a few images, none of which seemed similar to the one on my unit.

Wilt take a look at what you've posted there now.

Dutch061

Here is the wiring for a 7-pin harness (or at least what I have found as an Industry Standard), BTW on our 2020 400 BDL the harness comes in on the bottom where yours is on the top.

Black - 12V+
Green - Tail lights aka Running Lights
Red - Left Turn-Stop
White - Ground
Blue - Trailer Brakes
Brown - Right Turn - Stop
Yellow - Reverse Lights (not used with NuCamp)

Typically, they are of mixed sizes, with the 12V+ and Ground being 10-gauge, the Trailer Brakes being 12-gauge, and the rest being 14-gauge.

The Terminal Block is labeled, but the wiring isn't on the Terminal Block as it is on the labeling (on mine anyway).

It is funny, because this doesn't follow the 4-pin harness (other than ground) which are as follows.

Yellow - Left Turn-Stop
Green - Right Turn-Stop
Brown - Tail aka Running Lights
White - Ground

Brad

ScottG

FWIW, here is a labelled version of the image @Bayless linked to above. On mine--which appears to be wired a bit differently from yours--the positive stud is the second from the right and the 12V feed from the trailer pigtail is a heavy black wire.

CharlieRN

Thanks @ScottG, this was the photo I found as well. While the wiring connections in the J-box could have been moved around by the dealer when the Prodigy was installed, it is just as likely to have come from the factory wired differently than other T@B's.

One of the things I've found from comments and photos on this forum is that it appears that no two T@B's are completely identical. Wire runs & penetrations in particular seem to vary quite a bit from trailer to trailer.

Denny16

OK Charlie, sounds like you are good to go.  Though the dealer may have hardwired the controller’s power connection, but seems they didn’t.
 Cheers 

CharlieRN

I was finally able to determine that my J-box is wired similarly to that of @ScottG and @Bayliss, as shown in the annotated photo.

Specifically, the 12 v power via the 7-pole harness wire is to the second stud from the right. [Edit: you can't see it in the photo below, but there is a black wire obscured by the other wires that is connected to this stud] This makes sense, because one of the connections, the orange wire in the photo, runs to the breakaway switch (the other wire from the switch runs to the stud on the far left, which is the brake circuit). You can also see in the photo that there are two red wires; I've left them loose, but they also connect to the same stud.

One of them must be the circuit that connects to the house battery for charging when the camper is being towed, with the other perhaps going to the converter? My guess is that the heavier gauge of the two (the upper wire in the photo) is the one that connects to house battery. I'd like to disconnect that circuit to the battery as charging will now be via the DC-DC charger.

Appreciate any feedback or suggestions as to how to approach the issue.

ScottG

@CharlieRN, of the three cables coming into the box, which is which?

Denny16

Charlie, here is the wiring diagram for the 7-pin connections on a 2019 TaB320:
  The Red no 10,wire coming from the 7-pin cable connection is the 12VDC positive power wire from the TV.  This is what you want to disconnect to keep the TV directly charging the battery.  The other red wires on the trailer side are needed for the emergency breakaway switch and smaller red wire on the 7-pin harness is the left turn/stop tail light, which you need to leave connected.  Be careful, and put shrink wrap or tape on the disconnected power lead to prevent any shorts.

CharlieRN

ScottG said:

@CharlieRN, of the three cables coming into the box, which is which?

The bundle in the upper right is the 7-pole harness as installed by nuCamp. It is now collected zip tied to the frame, and plugged into the Prodigy. The smaller bundle on the lower right has just the two wires that go to the breakaway switch. Th bundle on the lower left goes to the trailer.

CharlieRN

Denny16 said:

Charlie, here is the wiring diagram for the 7-pin connections on a 2019 TaB320:
  The Red no 10,wire coming from the 7-pin cable connection is the 12VDC positive power wire from the TV.  This is what you want to disconnect to keep the TV directly charging the battery.  The other red wires on the trailer side are needed for the emergency breakaway switch and smaller red wire on the 7-pin harness is the left turn/stop tail light, which you need to leave connected.  Be careful, and put shrink wrap or tape on the disconnected power lead to prevent any shorts.

Thanks @De@Denny16. It looks like my wiring is bit different than this diagram though. For example, the hot lead to the breakaway switch is the pink wire connected to the second from right stud; the black wire to it connects to the 7th stud on the far left, to which the blue lead from the 7-pole harness is also connected.

If my 7-pole harness uses the same wiring color convention as per usual, the Left turn/brake connection is the 4th stud. You can see the red wire (barely) from th 7-pole harness in my photo. The red lead is consistent with what's shown on 7-pole wiring plug diagram I looked at, as well as in what you wrote.

The two red wires in my photo (shown loose) are to/from the camper, and connect to the second stud, to which the black wire of 7-pole is also connected. This is also consistent with what's shown on the wiring diagram I looked at (black wire for 12 VDC - the wire is unfortunately not visible in my photo.

Edit: I think what I am going to do is to test continuity from each of the two wires; they should be the same red wires that terminate in the cargo box and were previously attached to the positive terminal of the battery. They now are attached to a bus, so I can disconnect and test them one by one to each of the two red wires in the J-box. I'll post the results when done.

Denny16

Good idea, I was going to suggest using a multi-meter to test the circuits to confirm which one is which.
 Cheers