Disconnect battery when parked?

SlantedMark4 said
if I turn off the car and the battery is connected, there's still some load on the wires, right?

Seemingly conflicting answers, but the differences are actually easily resolved.

There is no load in the wires.
LOAD is power being drawn through the wires. With everything turned off, there is no load.

SlantedMark4 said
possible to cause a fire when the battery isn't disconnected?

Sure its possible. If there is a short to ground, or a cross wire short from feed to a something that wants electric power there could be sparks.
Those things are things that need to be fixed regardless. Route and secure cables properly. Check insulation for damage, etc.

SlantedMark4 said
I have to say, I've had two incidents with the wiring that almost ended in a fire (broken original amp. meter that ended pretty bad and a blown fuse)

The resistance in poor connections result in heat when current is trying to flow through them.
Fuses blow when current flowing through them exceeds their amp rating.

Murray said
On an old car, when the ignition switch is turned off, then everything is really turned off. There is no draw on the battery- things are OFF!

Murry is correct because he is describing draw, or load.

Bennoel 10 said
I don't think that is 100% true. If what you are saying then how would one turn on the four way flashers, lock the car on the side of the road and proceed to get help if say you ran out of gas ?? The interior light, horn, cigarette lighter, headlight and possibly a few other accessories will operate without the key in the ignition.

Those circuits are hot (potential), but there is no flow (current).

There must be a complete circuit for there to be current flowing. It's the current flowing that can be useful or cause damage.