Power transformer dual secondaries connection
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Figure 1. Multiple transformer configurations.

If there are four secondary wires then you have two independent 6 V secondaries. This is quite flexible and you can configure them in a variety of ways as shown in Figure 1.


0 - 6, 0 - 6 gives you two independent 6 V windings.
0 - 6, parallel gives you one 6 V output but with double the current.
6 - 0 - 6 gives a 'centre-tapped' output. This is used in some dual rail power supplies. Normally the centre-tap would be grounded.
0 - 6 - 12 is the same but the bottom terminal would be grounded.


You want the 0 - 6 - 12 arrangement. Because the current from both your circuits will return on the bottom winding it must be able to handle the sum of the currents. Post details in your question if you have further questions.







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Figure 2. Wiring 6 V and 12 V loads.