Hitch plug wiring problem

[dremelts]

The trailer batteries were not being charged while towing our trailer. A little probing with a voltmeter shows that I have full voltage on the charge wire at the front of the wiring harness but only about half voltage on the charge wire at the rear of the harness.



Should I take the time and effort to rip out the wiring harness to try to find the problem or should I just cut the old wire and run a new wire?



Everything else on the trailer connection works OK (brakes, tail lights, brake lights, turn signals).

 

[bmoeller]

Is there a break in the insulation on that wire allowing for easier access for corrosion? Are the terminals clean on the truck and trailer plug pins?

 

[jfrow2]

Originally posted by dremelts

The trailer batteries were not being charged while towing our trailer. A little probing with a voltmeter shows that I have full voltage on the charge wire at the front of the wiring harness but only about half voltage on the charge wire at the rear of the harness.



Should I take the time and effort to rip out the wiring harness to try to find the problem or should I just cut the old wire and run a new wire?



Everything else on the trailer connection works OK (brakes, tail lights, brake lights, turn signals).

Could be that the wire size is too small in which case it never has worked correctly--I doubt this your problem.



Very likely there is a bad connection-corroded or loose-somewhere on the line, not the wire itself.



Also very likely that there is a bad ground connection--the lights work because of their low current draw which results in low voltage drop. The battery when discharged is a large load and lots of current will try to flow, resulting in a large voltage drop.



Very unlikely that something has happened to the wire that has caused it to have more voltage drop. The most common thing that happens to the line is that it gets pinched, abraded, etc. which eventually goes through the insulation and blows a fuse.

 

[dremelts]

Re: Re: Hitch plug wiring problem

Thanks for the reponse... just want to clarify a couple of things.

Originally posted by jfrow2

Could be that the wire size is too small in which case it never has worked correctly--I doubt this your problem.

I know that it used to work - the trailer battery used to be fully charged when we arrived at our destination.

Also very likely that there is a bad ground connection--the lights work because of their low current draw which results in low voltage drop. The battery when discharged is a large load and lots of current will try to flow, resulting in a large voltage drop.

There was no load on the system when I took my voltage readings (I mean I did not have anything plugged into the trailer plug). I was getting the voltage readings by probing the wire thru the insulation. The reading I got at the front end of the wire was 12+ volts and the reading I got at the rear end of the wire was 6-7 volts. To my limited understanding of electronics that indicates that there is a load of some kind between the front and rear someplace. Now, I have to admit that I can't state positively whether my reading at the rear was before or after where the in-bed fifth-wheel trailer plug tapped into the line. I'll have to recheck that. If it was after the tap then the fifth-wheel plug could be the culprit.

The most common thing that happens to the line is that it gets pinched, abraded, etc. which eventually goes through the insulation and blows a fuse.

So, back to my question - if it is a problem with the wire is it better to just run a new wire to the back or try to find the problem with the original wire? It looks like a real pain to remove that wire loom - it goes in and out of the frame rail and is sandwiched between the frame and the fuel tank.



Maybe if I can eliminate the fifth-wheel plug as the problem I will just run temporary line to the back to test it. I guess if I did just run a new line I would be worried that eventually whatever caused the charge wire to go bad would also cause problems with the other wires in the bundle.



Anyway, thanks for your input.

 

[RustyJC]

The only problem I've had with the trailer wiring on my truck is the 7-pin connector mounted on the receiver was not weathertight. I was having some strange problems (the brake controller was showing that a trailer was connected when nothing was plugged in) that were solved by taking the 7-pin connector apart, flushing out the water and mud with WD-40, packing it with dielectric grease and reassembling it.



The water and mud packed in the connector were causing internal high resistance shorts in the connector between pins. Sounds like your +12V could have a high resistance short to ground - if so, this could be your problem.



Rusty

 

[jkern]

run a new wire

couple of reasons for this...



first the OEM wiring harness for trailer connectors is marginal at best on the size of wire run. i just re-did mine and i think the biggest wire in the bundle was a 16 guage... way too small to handle the 20 amps that the trailer brakes drw when fully engaged (the voltage drop was great and the wire will get quite warm on extended operation.



second: what you are trying to do (charging a remote battery) presents itself with a multitude of problems associated with large current flow (amps) and voltage drop because of the large current flow. if the battery in the trailer is "hungry" and you start the truck and the truck batteries are good batteries that are not really hungry. (this senario is living in the trailer for a couple days with the truck unplugged) then the truck batteries come up to the charged voltage (usually 13. 8volts) rather quickly. now here is the tricky part... the alternator sensing lead that attaches to the battery provides the alternator voltage regulator a way to "feel" the charge of the battery. if it is up to proper voltage then the alternator does not charge many amps... the more load you apply like lights, heater motor, etc, the more amps drawn from the battery which lowers it voltage... this is "felt"by the sensing lead and then the alternator puts out more amps to maintain the voltage at a constant 13. 8volts



so... what does this have to do with your trailer battery:



the battery in the trailer is connected far away with 20 or 30 feel of undersized wire and when this battery needs charging the voltage drop in the wire will cause this battery not to fully charge because it the voltage at the end of the wire may only be 11. 5 or 12 volts or less if there is high current flow. why is this, because the alternator senses that the truck batteries are fully charged and the voltage drop in the wire give the presumption that the rear batter is fully charged when it is actually near dead.



to easily solve you problem run a 12 or 10 guage wire (good for 30 to 40 amps) to the trailer battery. this will result in much less loss to the trailer battery



to solve the problem correctly you need a remote sensing alternator and battery isolater at the minimum which is $$$$ and the theory to understand it which gets into much more than even i understand or am willing to type here



i hope that i didn't confuse you too bad... but if you just run a new heavy wire, that will probably go alog way to helping you situation. be sure to take the advice of the other posts as well, and check all the wires and connections and grounds.



hope this helps

 

[jfrow2]

Re: Re: Re: Hitch plug wiring problem

Originally posted by dremelts

Thanks for the reponse... just want to clarify a couple of things.







I know that it used to work - the trailer battery used to be fully charged when we arrived at our destination.



>So we can say that the wire size is OK.





There was no load on the system when I took my voltage readings (I mean I did not have anything plugged into the trailer plug). I was getting the voltage readings by probing the wire thru the insulation. The reading I got at the front end of the wire was 12+ volts and the reading I got at the rear end of the wire was 6-7 volts. To my limited understanding of electronics that indicates that there is a load of some kind between the front and rear someplace. Now, I have to admit that I can't state positively whether my reading at the rear was before or after where the in-bed fifth-wheel trailer plug tapped into the line. I'll have to recheck that. If it was after the tap then the fifth-wheel plug could be the culprit.



>If some kind of load is drawing enough current thru a decent size wire to drop 12 volts down to 6-7 volts, something has to be getting very hot--you should be able to see and smell this.





So, back to my question - if it is a problem with the wire is it better to just run a new wire to the back or try to find the problem with the original wire? It looks like a real pain to remove that wire loom - it goes in and out of the frame rail and is sandwiched between the frame and the fuel tank.



>I still am not convinced that you need new wiring. For a voltage drop of 6 volts, there must be a high series resistance somewhere in the line, most likely, a bad connection. Also, are you sure you were measuring the right wire at the back of the truck?



Maybe if I can eliminate the fifth-wheel plug as the problem I will just run temporary line to the back to test it. I guess if I did just run a new line I would be worried that eventually whatever caused the charge wire to go bad would also cause problems with the other wires in the bundle.





>To answer you question, in the good old days before trailer wiring packages, we always had to run additional wires to the back of the tow vehicle, one to charge the towed battery and one for the electric trailer brakes, and sometimes another wire for a good ground. So, yes, it is quite possible to run a separate wire for the battery charging circuit in the towed. Just be careful with the placement of the wiring to avoid damage to the wire.



Anyway, thanks for your input.

 

[dremelts]

Found the problem

I pulled all the electrical tape off the area where they tapped the fifth wheel plug into the truck wiring harness.



The hitch shop that installed the plug went the cheap and dirty route of using those plastic tap connectors to tap into the main truck wiring harness. You know - the kind that you squeeze with pliars and it bridges the two wires by driving this little piece of metal thru the insulation on the wires thus making contact with the copper core of each wire.



Those things make tapping a wire very quick and easy and they will almost certainly outlast the warranty that the hitch shop gives you on their labor, but they will not hold up in the real world.



The trailer charge wire was so corroded that it broke in two when I removed the tap connector! (That explains the low voltage readings that I was getting). So I spent a couple of hours removing each tap connector, stripping the insulation off the wires, soldering the connection, and taping them up.



I guess I should be glad that it was the trailer charge wire that went out instead of the turn signals, brake lights, or the brake controller wire.



Regards,

Dave

 

[jfrow2]

Re: Found the problem

Originally posted by dremelts



... ... . I spent a couple of hours removing each tap connector, stripping the insulation off the wires, soldering the connection, and taping them up.



Regards,

Dave

In my book, that is the only way to make a good reliable connection for the RV

 

[klenger]

You can also buy butt splice connectors that have an environmentally sealed heat shink outer jacket.

 

[MCummings]

Re: Found the problem

Originally posted by dremelts

The hitch shop that installed the plug went the cheap and dirty route of using those plastic tap connectors to tap into the main truck wiring harness. You know - the kind that you squeeze with pliars and it bridges the two wires by driving this little piece of metal thru the insulation on the wires thus making contact with the copper core of each wire.

Scotchlock.



Merrick

 

[ndurbin]

The scotchlocks are worthless for exposed wires and alot of places seem to use them for that.

 

[Eric_77]

You can get the weather reisitant wire nuts that are filled with silicone when inserting the wires it pops the seal and the wires are coated in silicone providing a very tight insulation against water. Good enough for code to be buried for 100-220 voltages.