If I was in your situation, I would start checking at the fuse box to see what circuit was pulling power. Once you locate it, you can then figure out what is on that circuit to help narrow down what is running power.

Check the actual draw across each live circuit. Some are always hot but the current draw should be very small, in the milliamps. From the sound of things I'd guess you're looking for a draw of around 1 amp, maybe more, providing you have a beefy Group 49/H8 Pursuit battery in good shape.