For zinc coated plates, we should always use a low silicone type consumable for welding. Some manufacturer have wires that is especially built for welding on these primed plates, however they are not too popular. Safro and Oerlikon has got the product used for welding of zinc surfaces, they are the Safdual Zn, or Carbofil Galva.
Or in anycase if you have difficulties looking for these wires, you could opt for AWS: 5.18:ER70S-3 designated wires. With this general wires, expect porosity in the welds due to vaporisation of zinc which forms gas bubles in the weld.