How many watts are in 13 amps?

Excellent question. That depends on the voltage, for 120 VAC, the answer is 156 watts. PIE, Power (in watts) = current (amps) X Voltage . For 12 VDC, 15.6 watts. An interesting asside, if you ohms check a 120 watt (should draw 1 amp) incandesent light bulb, it will read much less than you would expect (120 ohms). Turns out, the filament at room temp is much more conductive.