Thanks Phil - I appreciate your response. It did make me re-read the above postings and then get back into 43.13, and as painful as that can be, a good refresher.

I would add two points hoping that others might find helpful.

1. current calculation web sites often are for cars and assume a frame ground is being used. If return wires are used, the complete circuit length is to be used in the calculations/charts.
2. a small weight savings can be had when putting strobe, position, nav, and landing lights in wing tips by using a common ground but the total current in the ground wire has to be used when sizing.

BTW - there was a very good article in one of the aviation mags (either Kitplanes or Sport Aviation) only a month or two ago discussing ground returns; the considerations when torn between using wires or a chassis ground. (In full disclosure I'm a proponent of wires and a common ground buss.)

BTW (and this is an IMHO input) there are lots of automotive and marine wires that are as good as aviation wire for the intended use. They are supplied to one or more commercial specs which have to be read to determine usability in an aircraft. In all cases, wire used in an airplane has to be plated - raw copper like lots of the stuff off the selves in you see in the local BB store is no bueno. BUT (#1) - it is much easier buying to a milspec so this is a non-value added comment. But (#2) - if you are stuck between a rock and a hard spot . . . . . . . .