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Old 06-25-2014, 09:46 AM   #15
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1977 31' Sovereign
Indianapolis , Indiana
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Posts: 52
When I connect a volt meter, I get between .05 and .09 volts. The red line is touching the ball of the truck and the black is touching inside the AS coupler.

I'm going to try this on another camper in a bit and I'll keep u posted.

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Old 06-25-2014, 11:14 AM   #16
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Cumming , Georgia
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The above test will tell you nothing since the tow vehicle and the trailer are not sharing a common ground point.

What you need to measure is the draw on the battery. I would suggest first setting your meter to the 20A range. Then, on your meter move the red test lead to the socket just above where it currently is (to the one marked "20A"). Then disconnect the negative batter cable on the tow vehicle....keeping the negative battery cable disconnected, you need to put your meter "in series" between the negative post and the negative battery terminal. Connect the black meter lead to the negative battery cable and the red lead to the battery cable you earlier removed from the battery post. With your meter setup in series with the battery you are now measuring the actual draw on the battery. Now connect your trailer and monitor what happens to the battery draw.

One note of caution while doing sure to close and keep closed all the door, keep the keys out of the ignition and make sure nothing is turned on in the tow vehicle. It's not hard to draw over 20A and blow the fuse in your meter if you're not careful.

Good luck!

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Old 06-25-2014, 11:16 AM   #17
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South of the river , Minnesota
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Originally Posted by jasonsherman View Post
Here's the problem:

I hook the hitch up to the AS and my truck batteries seem to discharge. The pig tail is NOT connected...only the hitch ball. It's happened at least 3 times and only takes about an hour for the batteries to need a jump. Truck batteries are in good shape. No problems any other time. Ideas?
The problem is in your truck, not your trailer. It doesn't matter whether the trailer is positive or negative ground. Most of the theories presented upthread don't make engineering sense. There's one (or possibly more) of four things going on:

1) Your truck has some sort of load leveling or ride control system that doesn't work quite the way it should, and the weight of the trailer is turning some part of it on, causing the battery drain.

2) Your truck has existing problems with its battery or charging system, and when you drive around with the trailer, the slight extra load of the trailer brakes, lights, and charge line is enough to knock over the house of cards. When you park the battery's already low, and an hour later the truck won't start.

3) You're in the habit of leaving something on in the truck when you park with the trailer and you don't realize it. Perhaps you leave a door open that results in the dome light staying on, or you run the stereo or some other load, or leave some other light on when parked.

4) There is some sort of intermittent wiring fault in your truck and the added weight of the trailer on the hitch stretches the frame just enough that the problem shows up. I believe the chances of this are extremely remote.

The way to find these kinds of problems is to 1) test the battery and measure its state of charge before parking to rule out problems there, and 2) connect an ammeter to one of the battery leads and monitor the current draw while parked. If an hour is enough to create a problem with a good, fully charged battery, you should see at least a 10 amp draw. Then pull fuses in the truck fuse box until the draw disappears, at which point you've found the circuit that is creating a problem.
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Old 06-25-2014, 11:17 AM   #18
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Connect the red test lead to the negative battery cable and the black lead to the NEGATIVE BATTERY POST.

sorry for the typo....
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Old 06-25-2014, 11:18 AM   #19
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Well said jammer.
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Old 06-25-2014, 01:05 PM   #20
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I see you have a ninety one ford diesel. Us there a secondary trailer hook up wire under the hitch that might be being pinched when weight is applied? My truck has a regular rv hookup and a blade type hook up underneath..can it be shorting? Jim
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Old 06-25-2014, 07:45 PM   #21
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2007 16' International CCD
orem , Utah
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Electric jack hooked up backwards maybe

That would be easy to do mine is black wire though goes to positive. There is no negative wire on my trailer to pwr jack.
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Old 06-25-2014, 08:07 PM   #22
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i've seen dome lights come on when a vehicle is put on a lift. it could be the added weight is causing a light (under hood light, door, glove box, or courtesy light is coming on.
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Old 06-25-2014, 08:40 PM   #23
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The frame of your coach is the negative side of the circuit for the tongue jack.
I agree that the problem is in the TV. If you have access to any type of trailer that has a similar or greater tongue weight. Perhaps you can duplicate the problem and eliminate your coach.
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Old 06-25-2014, 09:29 PM   #24
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Looks like we can rule out the trailer as a source of the current draw.
I pulled up the AllData wiring diagrams and specs for the truck in your profile. With a dual diesel battery system without an isolation relay, if the batteries are fully charged and in good condition it would take a huge draw to drag them down to the point where the engine wouldn't start in a short amount of time.
Take the truck into a good shop and have them do a proper charging and starting system test. I'd start with a battery capacity check with the batteries disconnected. According to AllData they are wired in parallel. The counter boy at AutoZone or Pep Boys won't have a clue as to how properly to set the handheld they use to check batteries.
After that the usual alternator output check, cable resistance and condition, and starter draw and connections.
You've got to start with the basics.

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Old 06-26-2014, 02:12 AM   #25
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We once had a GMC that discharged like that (only in far distant places after towing). We traced it to a short in the wire linking the two batteries. Dealer installed the second battery by routing cable behind radiator, enough miles and the chaffing resulted in the mysterious intermittent discharge ( and lots of heartburn)
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Old 06-26-2014, 04:36 AM   #26
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Truck batteries discharge

Way too many cooks in the kitchen. PM me if you have any questions I can help you with.

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