The thermoelectric power (TEP) and the electrical resistivity (ER) of Al-Mg-Si (balanced) and Al-Mg-Si-Cu (balanced + Cu) alloys have been measured in the temperature range 300-800 K. TEP and ER are found affected by different types of precipitates in the Al matrix. Addition of Cu refined the microstructure of the balanced alloy hence altered the TEP and ER measurements. Cu promotes the kinetics of artificial aging due to the formation of the Q' phase and the intermediate phases which precipitate at earlier temperatures. The coexistence of the equilibrium (3 (Mg2Si) and the stable Q-phases results in stabilization of the TEP at elevated temperatures. The existence of Cu slightly increases the lattice rigidity leading to a decrease in the rate by which the ER increases with temperature. Repeating measurements after slow cooling of the two alloys changed considerably the results of TEP and ER. Correlation was found between different types of precipitates and changes in the TEP and ER indicating the possibility of employing TEP and ER measurements to study the precipitation sequence in such alloys.