There are charts for determining what gauge wire you need based on amps and length, but I can't seem to find any. Based on my experience with a whole lot of wiring on a whole lot of different stuff, I'd say no, though. Assuming you're coming off of the battery cable connection on the starter solenoid, I'd want 8 or 10 gauge from there to the ignition switch, back to the small terminal of the starter solenoid (12 can be OK there, depending on solenoid), and over to the big lug of the alternator. Sometimes there's even a light battery cable between the alternator and solenoid. If the wire is too big, the only danger is loss of space and money. If it's too small, you lose power through resistance, resulting in heat.