Thermoelectric (TE) properties of a single nanowire (NW) are investigated in a microlab which allows the determination of the Seebeck coefficient S, the electrical conductivity sigma, and a full ZT-characterization in the validity limit of the Wiedemann-Franz-law (ZT-figure of merit). A significant influence of the magnetization of a 70 nm diameter ferromagnetic Ni-NW on its power factor S-2 sigma is observed. We detected a strong magnetothermopower effect (MTP) of about 10\% and an anisotropic magnetoresistance (AMR) as a function of an external magnetic field B in the order of 1\%. At T=295 K and B=0T, we determined the absolute value of S = -(19 +/- 2) mu V/K. The thermopower S increases considerably as a function of B up to 10\% at B = 0.5T, and with a magnetothermopower of partial derivative S/partial derivative B approximate to -(3.8 +/- 0.5) mu V/(KT). The AMR and MTP are related by partial derivative s/partial derivative r approximate to -11 +/- 1 (partial derivative s = partial derivative S/S). Hence, the TE efficiency increases in a transversal magnetic field (B = 0.5T) due to an enhanced power factor by nearly 20\%. (C) 2012 American Institute of Physics. {[}http://dx.doi.org/10.1063/1.4721896]