Possible Short Near Electrical Junction Box

Basil48192

I believe I have a bad/compromised connection near the black junction box on the underside of my 2021 T@B 320S.

Twice now (since returning from my last trip on some very rough roads) I've noticed that my batteries were not charging (via shore connection or solar).  

After ensuring that all my battery connections are secure, I crawled under the camper.  In both cases, after I 'wiggled' the wires coming out of the junction box, it started charging again.

I've now removed my batteries and covered my camper for the winter, but in the spring I will pull the cover off of that junction box.

I'm wondering if anyone has had a similar issue and if there is any advice as to how to disassemble the box.

Thank you in advance.

Bayliss

@Basil48192, I am not clear on what you mean by "disassemble" the box.  There are two screws to remove to open the cover and access the electrical terminals.  I have included the Forum "resources" link below.  Open the "Electrical Resources" link and scroll down to the "J-Box" info, which includes a photo of the interior, plus a diagram of what is connected to each terminal.  Yours is likely the same configuration.

Since you only mentioned an issue with shore power and solar, I'm not certain that the battery connection itself is the issue, but I'm thinking it is, because the converter "converts" AC power to DC power to charge the battery and supply power to the DC systems in the trailer.  Additionally, a bad connection at the J-Box is not likely to be causing an issue with the AC power.  On the other hand, it may be a loose ground connection at the J-Box.

You may just have a loose terminal nut that needs to be tightened down, a damaged wire to/from the terminal(s), or a bit of corrosion at one of the J-Box terminals.  If corrosion, you will want to clean that off the involved terminal(s) and maybe apply a very light coat of dielectric grease (such as "CRC") to the terminal(s), before replacing the terminal nut(s).  Specifically take a look at Terminal #6 (12V+) and Terminal #7 (12V-).  If you search "J-box" or "Junction Box" using the search box at the top of the Forum page, you will likely find discussions about troubleshooting those connections, or other suggestions.

IMPORTANT:  Before removing any nuts from the J-Box terminals, open the J-Box cover and wiggle the wires near those two terminals to see what happens, and which wire is likely involved.  Do that with only the 12V battery connected, and the disconnect switch "ON" so you know you have a connection to the battery.  Leave the 120V shore power and tow vehicle 7-pin cord disconnected.  Depending on what you find, before you remove any terminal nuts and/or wires, and before retightening the nuts and applying the dielectric grease, be sure to disconnect ALL power to the trailer so you don't get zapped.  Once  the electrical connections are re-tightened, reconnect your battery and see if that fixes the issue.

Another test, which you may actually want to do first, is to leave the trailer battery connected (with disconnect switch "ON"), shore power disconnected, but also connect the tow vehicle 7-pin cord and turn the tow vehicle ignition "ON".   Wiggle the J-Box wires and see if you make a similar finding when moving the wire(s).

NOTE:  If you have made any electrical changes to your T@B, your wire connections between the battery and the J-Box may be slightly different, so keep that in mind.

Good luck!

https://tab-rv.vanillacommunity.com/categories/video-resources

Basil48192

@Bayliss.  Thank you for the detailed response.  I put new, lithium batteries in it earlier this year, which I just removed and brought into the house for the winter.
I'll do my studying over the winter so I can start checking things out in early spring.  Thanks again!

CatDaddy

I agree with what @Bayliss has written. I will only add that the screws that hold the cover on the junction box are 10mm. The nuts on the terminals are also metric, perhaps 8mm. In any case, these are the only metric fasteners I’ve found on my 2022 320S BD. 

Your problem is way more likely to be a loose connection than a short. Shorts blow fuses snd melt wires. Loose connections cause intermittent issues.  

pthomas745

There are several threads with pictures and descriptions of the junction box wiring setup that might help.

https://www.google.com/search?q=junction+box+wiring+site:tab-rv.vanillacommunity.com&client=firefox-b-1-d&uact=5&oq=junction+box+wiring+site:tab-rv.vanillacommunity.com

Basil48192

Thank you all!