# wiring for dump trailer



## Black Jaque Janaviac (Mar 31, 2012)

The local cemetery let me use their dump trailer to haul their excess sand away.  The dump trailer has its own battery and I was told by the manager of the cemetery that it is supposed to charge off the tow vehicle.  Another time I was told by a young cemetery worker that the charge feature doesn't work.

Today the battery died.  We tried charging it with jumper cables but darn near burnt out the cables, and blew some fuses on my truck. 

After examining the way the battery was wired into the dump trailer I see they had a black cable running from the positive to a bolt on the trailer frame.  The negative terminal had two red wires, one coming from the trailer-light connector and the other going to the hydraulic pump. 

I understand now why I burnt out my cables and fuses.  My question is:  Is this the right way to wire the battery for the dump trailer?  Positive to frame, negative to hydraulic pump?


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## greg13 (Mar 31, 2012)

What type of trailer connector are you using? There are many configurations.


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## Black Jaque Janaviac (Mar 31, 2012)

It's the round 6 or 7 point connector.  I don't know why that would make a difference over which terminals were used.


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## nate379 (Mar 31, 2012)

Would work fine, though positive ground systems aren't very common, not sure what reason there would be?

If the battery was dead I could imagine it would warm up a set of thinner wire jumper cables after a few mins. Not made for that and not a good idea to "charge" a battery like that either.

To set it up to charge off the truck, would need a fairly heavy gauge wire.  The 14 gauge wire that the trailer plugs usually have isn't able to handle that much draw.


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## ScotO (Mar 31, 2012)

I never heard of a postive ground on a trailer.  The only way that would even be possibly feasible is if the trailer was completely insulated from the towing vehicle, which I highly doubt is the case.  Sounds to me like someone wired the damm thing wrong somewhere down the line.....


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## Black Jaque Janaviac (Mar 31, 2012)

> If the battery was dead I could imagine it would warm up a set of thinner wire jumper cables after a few mins.


 
I don't think it was the dead battery that heated up the cables.  It was the fact that the battery on the trailer was wired positive to ground (frame).  I didn't pay any attention to this when I connected the jumper - I simply connected like you would a normal jump.  Live positive to dead positive; live negative to dead ground (trailer fame).  

So there was a short.  It went from live positive to dead positive to frame to dead negative clip to live negative terminal.  Big sparks!


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## Black Jaque Janaviac (Mar 31, 2012)

> Sounds to me like someone wired the damm thing wrong somewhere down the line.....


 
Yeah.  I think they might pull the battery out and bring it in a garage to charge.  Then the part time help puts it back in the trailer - perhaps not paying attention to the poles.

OK good.  I had turned the battery around to the way that I thought should be correct and left it.  I later thought I'd check here to see if there might be a good reason to have a positive-to-ground.


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## ScotO (Mar 31, 2012)

Black Jaque Janaviac said:


> Yeah. I think they might pull the battery out and bring it in a garage to charge. Then the part time help puts it back in the trailer - perhaps not paying attention to the poles.
> 
> OK good. I had turned the battery around to the way that I thought should be correct and left it. I later thought I'd check here to see if there might be a good reason to have a positive-to-ground.


That would be a good start.  There is no reason that thing should be grounded positive.  Let me know how it works out for you when you wire it up grounded negative with a good charge on the battery.


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## fossil (Mar 31, 2012)

I have a dump trailer, and I just went out to check to make sure (although I knew I already knew the answer)...negative ground for the battery in the trailer for the hydraulics.  So long as the hydraulics aren't being run, there's no complete circuit through the trailer battery, so I s'pose you could get away with dragging the trailer around connected to the tow vehicle, using the trailer lights...they don't care about no stinkin' polarity.  You probably could have charged that battery if you'd have disconnected the trailer from the tow vehicle, and/or disconnected the trailer battery from the trailer.  But with it all hooked up, and the ground terminal in the cable plug connecting one battery's + terminal to the other battery's - terminal...nope. Sparks are gonna fly and things are gonna fry.  Rick


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## nate379 (Mar 31, 2012)

Yeah I didn't even think of that.  It would probably be ok as far as going down the road, but run the pump with the trailer hooked up and it would likely short through the ball and hitch.

Some heavy equipment is positive ground, and old cars/trucks often where, but I don't see a reason for that trailer to be other than someone screwing up.



Scotty Overkill said:


> I never heard of a postive ground on a trailer. The only way that would even be possibly feasible is if the trailer was completely insulated from the towing vehicle, which I highly doubt is the case. Sounds to me like someone wired the damm thing wrong somewhere down the line.....


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## greg13 (Mar 31, 2012)

Black Jaque Janaviac said:


> It's the round 6 or 7 point connector. I don't know why that would make a difference over which terminals were used.


 
There is 7 pin flat pin (RV type) There is 7 pin round pin (Tractor trailer type), There is small 6 way round pin, there is 4 pin round, and 4 & 5 pin flat type connectors. These are the common type connectors, all can be wired different. The most common type for that application is the RV type, that can be wired with a hot terminal to charge the battery. I have never seen a positive ground system for a dump trailer, that would be asking for trouble. The only reason I could think of may be the pump was set up backwards and by switching the motor to positive ground would reverse the DC motor direction (This will not work on an AC motor). The other problem you have with RV type plugs is the color codes are not standard so you have to pay close attention what the wire does and not the color of it.


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## ScotO (Mar 31, 2012)

bottom line fellas is the fact that the trailer, being wired (accidentally or not) positive ground is not compatible with the negative grounded vehicle it is hitched to.  Someone made a BOO-BOO when they wired that battery positive ground...


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## greg13 (Mar 31, 2012)

Here's a link for the connector wiring diagrams


http://www.etrailer.com/faq-wiring.aspx


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## KodiakII (Apr 1, 2012)

Scotty Overkill said:


> bottom line fellas is the fact that the trailer, being wired (accidentally or not) positive ground is not compatible with the negative grounded vehicle it is hitched to. Someone made a BOO-BOO when they wired that battery positive ground...


 

My thoughts exactly!  No matter what you do it is going to ground through your tow vehicle and then short out.


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## MasterMech (Apr 1, 2012)

No trailer built to be towed by any vehicle manufactured in the last 60 years should be wired for positive ground.

Fossil is correct in that the lighting wouldn't matter as far as polarity is concerned. Heck the Hydraulic motor might even run but the controls would be reversed. But connecting the battery to the 12v neg. ground tow vehicle would result in a dead short. Be glad a few popped fuses is all that happened. Usually batteries scream in agony, wiring goes up in flames and alternators leave a "Dear John" letter.

The dipstick that put the battery in backwards in the first place should have noticed that the cable terminals didn't fit the posts the same as the old battery.  Positive terminal/post is noticeably larger than the neg. unless someone shaved the pos term down to make a neg term fit.  Happens.


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## ScotO (Apr 1, 2012)

MasterMech said:


> Fossil is correct in that the lighting wouldn't matter as far as polarity is concerned.


If you have LED lighting on your trailer, it does matter.  LED's are polarity sensitive, incandescent lights are not.


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