Maybe this has been answered already, if so maybe someone can point me to the post.We're on a 3 week cross country trip with the kids in a 31' Jayco travel trailer. Had our battery system give us some trouble today while entering New Mexico from Texas. At a rest stop for lunch, we noticed our refrigerator had stopped working on LP. Looked into it and discovered we had no 12v anywhere in camper. Just got into the campground about an hour ago (in a heck of a thunder and lightning storm) and when we hooked up to 30 amp AC, I still had no 12v systems working. After fooling around and looking at it for over 2 hours, I discovered that if I disconnect my battery, my 12v systems work. Very strange to me.The short of it is the following:- Battery is fully charged (brand new last week).- All fuses and breakers test good with multi-meter.- I get 12v between the positive fuse holder near the battery terminal and frame.- I have no 12v input into the converter from the battery leads at the rear of the converter.Anyone ever run into something like this before? PS...had to create a new login identity. On the road and I can't remember my sign in credentials...but I'm a regular here on RVnet. Best thing to come about since camping itself!

By any chance did you reverse polarity on the new battery?That can really toss a wrench into your 12V system.

"discovered that if I disconnect my battery, my 12v systems work. "How exactly do you "disconnect"? That might help with this.I am hoping you did not just get the wrong way for using the "battery disconnect switch", so when you think you "opened" it, you actually "closed" it, so now everything works!!! :) (That would be something I would do when under stress, setting out.)

BobsYourUncle wrote:By any chance did you reverse polarity on the new battery?That can really toss a wrench into your 12V system. x2 sounds like you connected the new battery up backwards. Good luck,Bill

By disconnect, I removed the negative battery cable. Set-up is stock from Jayco, no disconnect or switch.New battery was installed by our local RV dealer.I did remove the battery and then reinstalled it. Would removing the battery and then reinstalling it lead to something like this? As far as reversing the polarity, I'm pretty sure I didn't reverse it at any time...black is + and white is -. Also, the reverse polarity fuses in converter are still good (per multi-meter).I've been thinking some more on this, and perhaps I should share this...full disclosure.As I mentioned, I removed the battery and reinstalled it. The reason I did this was to jump the tow vehicle...I'll explain:Our youngest, somewhere between Amarillo and Roswell, decides he needs to use the restroom. We pull off the road and all take turns using the lav in the trailer (12 volt system working as the water pump was functioning). When we get loaded back up and go to start the tow vehicle, I get nothing...no turn over, no clicking, nothing. So, being in the middle of no-where, I decide to jump off the deep cycle battery. I remove it from the case, jump the truck, then reinstall it. Never checked to see if it was working...but at our lunch stop 2 hours later, nothing is working.I was surprised that the truck wouldn't start. Battery in truck was in fairly good shape... Could an electrical problem with the trailer battery pull down the tow-vehicle battery?

jfeltham wrote:Could an electrical problem with the trailer battery pull down the tow-vehicle battery?You were likely operating off the tow vehicle all along. There is a connection through the trailer connector to charge the trailer battery while towing.The phrase "brand new battery" translates about 50% of the time to "electrical system problem" to me. A new battery is often the first thing changed when there is a problem, and things will work for a while because the new, charged battery covers for the rest of the system.You might want to check your tow vehicle fuse for the trailer 12V line. Then start by measuring the battery both connected to the trailer and unconnected.

Connecting Battery Kills 12v System | Good Sam Community

dougrainer
Nomad
Jul 27, 2018
jfeltham wrote:
dougrainer wrote:
On Jayco, there is a 30 amp ATC fuse. This fuse is between the Battery and the INSIDE fuse panel. It is located in 2 places depending on the Year Jayco. On a short pigtail within 10 inches of the POS post of the battery. OR, on the front of the trailer ON the cross frame, there is a 4 by 4 metal box and coming out of that box is that 30 amp ATC fuse. IF that fuse is blown(it is) replace it, Your problem is solved. Also, if that fuse is blown, your truck will not charge the battery in transit. Doug

30 amp fuse on POS line is good.
So strange. everything works as it should when connected to 115v.
Shut off 115v and connect the battery, and all 12v stops working whether or not 115v is connected.

Follow-up question...what is the Yellow line on the NEG cable? It has a 35amp in-line fuse. When connected, it gets very warm.

You have already figured it out. You have the POS and NEG wires reversed at the battery. THAT will teach you to not label or take a pic of the cables before you disconnect them. Doug

PS, the yellow wire is usually the tongue jack fuse. It is wired direct to the battery.
troubledwaters
Explorer III
Jul 27, 2018
MrWizard wrote:
Trace the two wires is where they go
If I had to make an emg guess
Fused wired positive
Other one ground/neg
My guess (since we're all guessing here) would be both of those black wires go to different devices (like slide motor & tongue jack, for instance) and both devices are grounded to the frame; hence both black wires would go to the Positive batt terminal.
2oldman
Explorer II
Jul 27, 2018
CA Traveler wrote:
Lesson learned? Mark all wiring and take pictures before disconnecting.
x2. To others reading this, please do that. You will not remember which wires go where.
BFL13
Explorer II
Jul 27, 2018
"New question: the second set of leads to battery...I'm assuming they are for the brakes, running/tail lights? They are both black and one is fused. Any idea how to connect these? I don't want to experiment for fear of really messing something up."

There should be one pos wire for the emergency breakaway --this wire is not to be fused and goes on the trailer battery pos post.

The pos post would have two more pos wires--one from the DC fuse panel/converter, and another for the slide (which will have a fuse)

The 7-pin #4 pin connects to the trailer battery too, but is likely joined to the pos wire from the fuse panel somewhere near where that wire is fused before it goes to the pos post.

The power for the front jack(s) is also probably on that same pos wire coming from the DC panel along with the 7-pin #4 but will have its own 30 amp fuse.

If you have a solar controller, its 'batt' pos also goes on the pos post and so will the pos input to any inverter you have. Too many lugs stacked up! So use a buss bar to take the various pos lugs and one fat wire (fused) from the pos buss to the pos battery post.
wnjj
Explorer II
Jul 27, 2018
Running lights have nothing to do with the trailer battery but there should be something the connects to the breakaway switch to power the brakes in the event of hitch separation. I think that one may not be fused. The other could power something like an electric hitch jack or slide room. Those black wires may both be positive but trace them before connecting.
CA_Traveler
Explorer III
Jul 27, 2018
Lesson learned? Mark all wiring and take pictures before disconnecting.
MrWizard
Moderator
Jul 27, 2018
Trace the two wires is where they go
If I had to make an emg guess
Fused wired positive
Other one ground/neg
jfeltham
Explorer
Jul 27, 2018
Made some progress this morning. Looks like my understanding of which leads from camper to battery are mixed up and I probably connected them wrong.
I traced the leads from converter to battery and found I had both positive and negative lead connected to NEG battery terminal (honestly don't know how I did that). 12v system is working fine now that I have white to NEG and black (which has a yellow pigtail with 35amp fuse) to POS.

New question: the second set of leads to battery...I'm assuming they are for the brakes, running/tail lights? They are both black and one is fused. Any idea how to connect these? I don't want to experiment for fear of really messing something up.
jfeltham
Explorer
Jul 27, 2018
dougrainer wrote:
On Jayco, there is a 30 amp ATC fuse. This fuse is between the Battery and the INSIDE fuse panel. It is located in 2 places depending on the Year Jayco. On a short pigtail within 10 inches of the POS post of the battery. OR, on the front of the trailer ON the cross frame, there is a 4 by 4 metal box and coming out of that box is that 30 amp ATC fuse. IF that fuse is blown(it is) replace it, Your problem is solved. Also, if that fuse is blown, your truck will not charge the battery in transit. Doug

30 amp fuse on POS line is good.
So strange. everything works as it should when connected to 115v.
Shut off 115v and connect the battery, and all 12v stops working whether or not 115v is connected.

Follow-up question...what is the Yellow line on the NEG cable? It has a 35amp in-line fuse. When connected, it gets very warm.
jfeltham
Explorer
Jul 27, 2018
2oldman wrote:
jfeltham wrote:
On the road and I can't remember my sign in credentials...
Shouldn't have to. Your browser should.

Different computer, different browser. Should have linked them to my Google/Chrome account but haven't.