It depends. Some truck manufacturers have power available only when the key is on, or in my case the motor is actually running.

Some trailer manufacturers and conversion companies wire their trailers differently. Some will only use the truck's battery to directly power the stall and tack areas, Some will power everything, some will only power the LQ batteries in a recharge situation. Other trailers are totally stand alone, and not need the truck for any electrical function.

These variances can occur depending on the age of the trailer, the trailer's brand, and the conversion company. Not all will be the same.

Thanks Gard, so where would I start in figuring how this thing is wired?  Here is what I know, the guy I bought the trailer from said that the batteries never charged well for him so he added a charger, a small box with a plug.  There are wires on both batteries that go to the charger and a single wire that goes into a little hole on the trailer....where it goes from there is a mystery.  It would appear the only way to charge the batteries is the added charger or could the mystery wire be two ways and charge when the trailer is plugged in?

Most trucks only offer a trickle charging, not enough to replenish depleted LQ batteries.

You can find out the single wire's source by using a multi meter. When it is on the battery, you will have a voltage of ~12.5V. When it's disconnected and your truck is running, and if you read 13.8V, this is the charging wire from the truck. If there is no voltage, it is the 12V feed wire FROM your battery to the trailer.