Perfectly normal to see +12.xv between disconnected negative battery cable and the negative battery terminal (assuming positive terminal still connected). When one terminal of the battery is disconnected (engine not running), there is no current flowing through any circuit in the car. When there is no current flowing there is no voltage drop across any of the resistive circuits; when measuring with the voltmeter they will all behave as wires directly connected to the positive battery terminal and the entire circuits (including the negative battery cable lead) will be at the same potential (12.6 volts or so) with respect to the disconnected negative battery terminal.

Chuck, you need to go back and read big red's advice. Measure the current draw on the battery with the engine off. To do this, you need to make sure your multimeter is set to measure current, and that the leads on the multimeter are plugged into the appropriate sockets to measure current (Amps). If you set the multimeter up to measure amps you should not be seeing 0 amps as the meter should be sensitive enough to pick up the current from the clock or a dome light.

Remember that when measuring current, the two leads of your meter will be essentially connected together (since current is measured in series with the load). So don't put the leads across the positive/negative terminal of the battery until you switch the multimeter back to voltage measurement!
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85 245 DL - 91 Mazda MX6 Turbo