[DAVID GAGNARD]

For 12volt current, you want a multi strand wire, the more strands the better,hence the welding lead cable. Just the opposite for 120/220v home use,for that, the correct application is a single strand wire.....

On my 65 coupe race car, battery is mounted in the trunk,if I remember correctly,I used about 16 to 18 feet of wire from the battery to the starter solenoid, I used a #1 or #2 welding lead,don't remember, but it is about 1/2 or a little more outside diameter,have not had any problems in 8 years!!!!!!!!
I actually ran it in a rubber garden hose so it would be somewhat protected from vibration and chaffing....

David