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Old 07-12-2016, 07:07 PM   #1
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Question 12 volt question...

We purchased a used 2002 Jayco travel trailer after over 2 years of not having a camper...we sure missed this lifestyle.

Naturally when buying something used we buy the old owners problems. So far we had to have the seal around the slide replaced, replaced one of the springs in the awning, had all the roof seams resealed, etc...

The problem the perplexes me the most is the 12 volt system. I upgraded the battery to a new deep cycle unit. When the rig is plugged in to the 120 volt system all the 12 volt related stuff works great. When I unplug the coach all the 12 volt dependent stuff dies. No slide, no lights, no fridge or anything else. I checked and all the 12 volt fuses are okay. I have tried just about everything to figure out what the problem is with no luck. Does anyone have any ideas please???

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Old 07-12-2016, 07:24 PM   #2
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Check for a fuse directly between the battery feed and the trailer.
Mine is visible behind the battery box just before the wire harness enters the underbelly.

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Old 07-12-2016, 07:36 PM   #3
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I am taking it for granted that your battery connections are WHITE (Negative) and BLACK (Positive).

- Make sure that the NEGATIVE battery terminal's cable goes down to the frame. Also, make sure that the cable connect to the frame is clean and tight.

- Does your TT have a 30 Amp main fuse by the battery? IF so is the fuse holder clean or corroded? While checking the fuse holder out, and your shore power connected, with your volt meter, and the fuse out, check to see if you have 12VDC on each of the connectors in the fuse holder. You should have voltages on each connector, the connector going toward the TT will have 12VDC from your TT's battery charge controller. On the fuse holder connector toward the battery should have 12VDC from the battery.

- When you say you checked the fuses, did you use a volt/ohm meter to check them? You would be surprised at how many members said that it looked good, but when they checked them with a meter they were bad.

- If you do not have 12VDC on the TT side of the fuse holder your problem is between there and the TT's charge controller.

- Let us know the mfr and model of your TT's battery charge controller as it may have a reverse polarity fuse that has blown.

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Old 07-12-2016, 07:58 PM   #4
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Along with the great advice already given; while you are checking fuses, pull the panel and check for fuses in the charge controller/converter itself. Don't ask me how, but when these blow, it is possible for everything to work while plugged in and nothing to work when unplugged and on battery only.
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Old 07-12-2016, 09:18 PM   #5
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Good advise above. Check to make sure the battery is hooked up correctly. Even if it was hooked up backwards even for a moment, you will blow the reverse polarity fuse. That fuse is in the main 12V fuse panel. Also check, for an inline fuse, near the battery.
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Old 07-13-2016, 04:49 AM   #6
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I know I hooked the new battery correctly when I installed it but I don't know if the people who we purchased the TT from did as they told us they installed their battery just before we arrived when we came to look it over.

I did check the main 30amp fuse numerous times and its still in good shape. I was unaware of any other fuses however. One thing I noticed was that when the coach is plugged in the 45amp converter makes all kinds of noise. I'm thinking of replacing it just to quite it down. I replaced, with new, all the 15amp fuses in the control board so I know they are good.

I'll do the tests that Don mentioned in his posts. Thanks for the ideas.
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Old 07-13-2016, 05:54 AM   #7
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What I do to be absolutely sure is to look for the word NEG or the Symbol '-' stamped on the 12V battery case and hand trace the NEGATIVE TERMINAL cable and make sure this is the one going to ground... Cables get reversed very easy with the RV world using the same battery terminal size for both polarities. I have purchased the same model replacement battery and found the manufacturer has moved the terminals locations which makes the cable wrong polarity to fit... Anyone not being observant will hook these up backwards everytime...

You see either WHITE and BLACK cables being used as well as RED AND BLACK cables.

In the RV WORLD WHITE is always GROUND and BLACK is HOT +12VDC


If these wirings get REVERSED than FUSES get blown between the battery terminals and the 12VDC Power Distribution Panel. Most of the time the REVERSE POLARITY fuses are on the 12VDC Power Distribution Panel but in some cases these may be located on the Converter/charger unit itself...

Even if you accidentally spark the cables when hooking up may blow these fuses...

Another walk around test I do alot is measure across my battery terminals with a multimeter and I will read 12.6-7VDC if the batteries are full charged and no Shore Power is turned 'ON'. Then I will turn 'ON' Shore Power and this DC VOLTAGE across the Battery Terminals will jump up to 13.6VDC or higher depending what mode the Converter/Charger starts up when first turned 'ON'. This tells me all is working normal and all fuses etc are OK...

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Old 07-13-2016, 04:17 PM   #8
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Great info...thank you. I've been building cars and other modes of transportation for over 50 years but its always nice to be reminded of this kind of thing. I will recheck my polarity just to be sure. Thanks again!
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Old 07-15-2016, 01:52 PM   #9
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Well I went and checked my battery and its hooked up as it should be. I ordered a new 45 amp converter today as the one in my coach screams when its plugged in. I suppose its just worn out and wants to retire. I have not had time to do all the great suggestions to my 12 volt problem but I'm hoping to get some time on Saturday. I'll keep you all posted....
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Old 07-15-2016, 02:40 PM   #10
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All good advice above. Grounds and fuses are usually to blame. Did you put a volt meter on the panel to confirm you have 12 v there? If you pull the 4 screws holding the control panel in you can get to the main connections from the battery.

From there back it's pretty simple and limited in what it could be from there.

Good luck and hope you find your issue.


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