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

2oldman
Explorer II
Sep 05, 2014
spacebetty wrote:
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?
Only fans and pumps care about 12v polarity.
spacebetty
Explorer
Sep 05, 2014
smkettner wrote:
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 :B

And 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 ;)

I don't use a generator, but I do use a smart charger plugged into house power. Do you think I need a larger gauge wire for that? Also, just curious, what is the purpose of the fuse on the positive cable?
spacebetty
Explorer
Sep 05, 2014
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).
wa8yxm
Explorer III
Sep 05, 2014
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.
time2roll
Nomad
Sep 05, 2014
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 :B

And 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 ;)
agwill
Explorer
Sep 05, 2014
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?
2oldman
Explorer II
Sep 05, 2014
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.

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Need help with my sketchy battery cable situation

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