Connecting Battery Kills 12v System

jfeltham wrote:
On the road and I can't remember my sign in credentials...

Shouldn't have to. Your browser should.

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

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.

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?

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

"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.)

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