Originally Posted by jasonsherman
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.