I was about to replace my 2 12v marine batteries with 2 6v deep cycles, when I realized the cable situation seems strange and possibly scary. But I don't know much about battery cables, so maybe it's fine. Here is a photo of the cables in question: The red cable is obviously +, and the white one with black on the end is -. The first sketchy thing is how the ends of the cables are all taped up and homemade - WTF? How do I know if they're an appropriate size? Also, there is a thin black ground wire coming from the taped up part of the + cable, which is bolted to the trailer frame. Why would the + cable be grounded? Isn't that what the - cable is for?! The 2 cables that were used to connect the 12v batteries in parallel are also of this taped-up homemade variety. I was going to use one of them to connect the 6v in series, but now am unsure whether I should use ANY of these cables at all. Wiring in new cables seems really daunting because I can't see an obvious way to access where they run up into the bottom of the trailer.Blargh! Any thoughts?

Most trailer wires are small because they're not expected to carry heavy loads, like big inverters. Lights and water pumps don't require much electricity.

Welcome to the world of trailer wiring. Yes you would think red would be hot but as you have found there is a wire that is black that goes to the frame. Guess what the white is hot and the red is ground. Prove it by plugging in your trailer without the wires hooked up. Measure from ground to each wire the white will be +12v I bet and there will be no voltage on the red to ground. The size wire looks no bigger that #8 might even be #10 which is too small to use with two 6 volt battery's in series to join. It is ok for limited use but you really should use standard size like you car or truck has. Where is your inline fuse from the battery? You should have one right at the battery before it goes into the trailer! Do you have a volt meter?

Cut all that tape and junk off. Get some crimp butt splices with heat shrink, heat gun, marine tinned wire of same gauge and of proper colors, closed lug ring terminals that match both the battery stud and wire, weather tight fuse holder for the positive side, heat shrink tube as needed in proper colors, quality wire crimper.... and get busy :BAnd if you ever charge from a generator replace the entire battery loop with #4 marine cable and update the converter as needed.Now you are sorry you asked ;)

The ends of the cables are taped up to indicate which is which, Though I do agree it LOOKS scary.. Ill bet if you remove the tape the wire is in good condition. The ends may or may not be factory or home made.. Frankly,, IF I crimp a connector on with the tools I have it is every bit as good (if not better) than a factory crimp.. But then I have professional grade tools that I paid well for.. they work nice too. I have several terminal crimpers.. Some are not so good But my West Mountain ratching job is absolute factory or better quality.. My GB is the #1 field crimper.

agwill wrote:Welcome to the world of trailer wiring. Yes you would think red would be hot but as you have found there is a wire that is black that goes to the frame. Guess what the white is hot and the red is ground. Prove it by plugging in your trailer without the wires hooked up. Measure from ground to each wire the white will be +12v I bet and there will be no voltage on the red to ground. The size wire looks no bigger that #8 might even be #10 which is too small to use with two 6 volt battery's in series to join. It is ok for limited use but you really should use standard size like you car or truck has. Where is your inline fuse from the battery? You should have one right at the battery before it goes into the trailer! Do you have a volt meter?This trailer is from 1978 and the batteries are not hooked up to charge when it is connected to house power (110v). I charge them by connecting them to a smart charger. So I don't think I can use this method to test which wire is hot... however, when the 2 12v batteries were hooked up, they worked with the red one on the positive terminal and the black/white one on the negative. Could they have still worked this way if what you say is true?There is no inline fuse, at least not before the wires disappear into the underside of the trailer.I do have a voltmeter (a multimeter).

Need help with my sketchy battery cable situation

27 Replies

dan-nickie
Explorer
Sep 17, 2014
Based on how this thread has been going so far, I would suggest you get someone out there that knows about trailer wiring right away.
spacebetty
Explorer
Sep 17, 2014
westend wrote:
It's not wise at all. Your lights operate off the 12V system, regardless if they work when plugged into the 120V AC. You need to remove those burnt and inoperative wires, install, a fuse or circuit breaker near the battery, and rewire the trailer up to the distribution panel. You need operating battery connections and an operable 12V system to move the trailer. Without 12V, you have no operating emergency break away system.

To someone unfamiliar with RV wiring or wiring in general, this may all seem like an insurmountable task but it's not. If you don't want to pay an RV specialist to do the work, start asking around to find a person conversant with electrical systems. You should be able to find a friend or a friend of a friend to help you out with this. If you decide to reconnect the batteries with the known, burnt wiring, there is a real chance that you will start a fire and possibly burn your RV to the ground.

I'm sorry, but there's no real NICE way to advise you on this, you need to fix your wiring issues. It's not that big of a job.

Maybe, if you listed your location, one of the guys on here would offer to help.

I apologize for being unclear. What I meant was that I have some string lights running off the 120v AC system (along with all my appliances), so it doesn't matter if I'm unable to use the 12v lights for a time.

What I was asking about the water pump is, can I bypass the existing wiring completely for now and run a new wire straight from the batteries to the pump, with a fuse of course.

I do have a friend who works as a plumber and knows some electricians. She is working on getting me in touch with one of them. I'm just looking for a temporary fix until I can get it done for real, because living without the water pump is annoying.
spacebetty
Explorer
Sep 17, 2014
RJsfishin wrote:
Quote:
My advice ?
Despite the wiring mess you have, it was working, so don't fix it. But DO add a fuse in the positive wire at the battery !!!!

Haha, well there was a burned out wire, insulation melted off it and everything, so I would hardly say it was working properly! I will definitely not use it as-is, even with a fuse installed.
Chris_Bryant
Explorer II
Sep 17, 2014
That small box was most likely a breakaway switch for the trailer brakes.
RJsfishin
Explorer
Sep 17, 2014
Quote:
It's not wise at all. Your lights operate off the 12V system, regardless if they work when plugged into the 120V AC.
--------------------------------------------------------------
Be careful of statements like this, which is not true of most all old RVs !

It was inconsiderate of the OP to post the black wire going to the frame, when in reality IT DID NOT. Most this thread was wasted because of this "mistake????"

My advice ?
Despite the wiring mess you have, it was working, so don't fix it. But DO add a fuse in the positive wire at the battery !!!!
westend
Explorer
Sep 17, 2014
It's not wise at all. Your lights operate off the 12V system, regardless if they work when plugged into the 120V AC. You need to remove those burnt and inoperative wires, install, a fuse or circuit breaker near the battery, and rewire the trailer up to the distribution panel. You need operating battery connections and an operable 12V system to move the trailer. Without 12V, you have no operating emergency break away system.

To someone unfamiliar with RV wiring or wiring in general, this may all seem like an insurmountable task but it's not. If you don't want to pay an RV specialist to do the work, start asking around to find a person conversant with electrical systems. You should be able to find a friend or a friend of a friend to help you out with this. If you decide to reconnect the batteries with the known, burnt wiring, there is a real chance that you will start a fire and possibly burn your RV to the ground.

I'm sorry, but there's no real NICE way to advise you on this, you need to fix your wiring issues. It's not that big of a job.

Maybe, if you listed your location, one of the guys on here would offer to help.
spacebetty
Explorer
Sep 17, 2014
Ok, not sure if anyone will see this but update is that there was no fuse, the red wire is positive, and it wasn't grounded- that little black wire goes to a small box attached to the frame right there. No idea what it's for. I would post a pic but it's irrelevant because there's no way I can use this system as is. I found a burned wire in the mass of wires inside the small panel cut-out where the battery leads enter the underside of the trailer.

New question- how crazy would it be to run temporary wires from the battery to the water pump fuse in my fuse box? And how exactly would I do that? I can't afford to pay for rewiring and don't trust myself to do it. The water pump is all I really need battery power for right now since I have lights hooked up to city power.
joshuajim
Explorer II
Sep 06, 2014
I think that the assumption that the black wire is grounded may be wrong. Only the OP knows for sure, but per the attached pic, it seems to continue past the "ground bolt". Could be a feed to an electric jack or a connection to the charge wire in the umbilical.

Also from the size of the taped up area, it may contain an inline fuse.
dan-nickie
Explorer
Sep 06, 2014
spacebetty wrote:
dan-nickie wrote:
Are you 100% sure the red was on positive before you disconnected them?

With the small black connected to the red and frame, I just don't see how that could be?

I'm absolutely sure. And my water pump worked!

Weird. I hope you get it figured out.
spacebetty
Explorer
Sep 06, 2014
Ok, when I get off work I'm going to westmarine for some wiring supplies. When I get home I'll take a closer look at what's going on and post again with more questions, I'm sure :-) Thanks for all the help so far y'all!

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Need help with my sketchy battery cable situation

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