current draw

prior to hooking up to tv, when I connect battery to trailer I get quite a spark, indicating a substantial current draw, everything is turned off but the radio light comes on. what could be using that much juice?

When you connect the battery, is shore power plugged in? Even so, there may be a spark. Consider this analogy:
Take a water hose. Attach it to your house. Make sure the nozzle on the other end is turned off or use a cap to cap off the hose. Turn on the faucet. Water will surge into the hose until the pressure equalizes with that of the house water line. Now, consider the battery as the house and the wires as the hose. When you connect the wire, the electrons in the battery surge into the wiring until the system reaches equilibrium. The very small draw of the radio, the CO/LP detector, the refrigerator electronics, the thermostat electronics are not what is causing the spark.

To eliminate it, consider installing a battery disconnect switch in between the negative terminal of the battery and the cable. Then you can just flip a switch and you don't get the visible spark. I don't know if there is one inside the switch. However, the switch may make the connection fast enough that it does not have time to generate a visible spark.

In my mods (link below), you can see the battery disconnect switch I installed.

No a/c plugged in.

All these devices have capacitors in them for noise and surge filtering. The initial surge is the capacitors charging.

Sorry Stephen.......didn't read your response above thoroughly enough.... I learned something today! It's a good day!