...I would like to know what gauge wire I should use to wire it. A friend of mine gave me some 12 gauge audio primary wire with the silicone insulation on it and I wanted to know if that wire would be OK to use, or are the strands in it too thin?...
The
AWG Wire Gauge Calculator is a useful and user friendly voltage drop (wire size) calculator recently linked by
timthescarred. Scroll down below the table. Set the "Select Voltage" dropdown box to "12 VDC or 1-phase AC" and enter
one-half of the anticipated length of the wire run between the power source and the pump (this compensates the calculator for a single power wire, since the chassis/frame will serve as the return ground path). Enter the posted current draw of the fuel pump. Now, experiment with different wire gauge sizes so that the "Percent Voltage Drop" window does not exceed 4% (~0.5 v).
Used as a power feed, the strand count of the wire is immaterial and only increases flexibility. Your concern should be whether the insulation of the wire will withstand abrasion, heat and corrosive road salts. Automotive applications typically use GXL, SXL or GPT insulated wire for their superior abrasion, heat and chemical tolerance characteristics.