Inspecting the wire gage table as defined throught the Bureau of Standards
Handbook 100, one will find that as the wire sizes become smaller (larger
gage numbers), every third gage number results in one-half the
cross-sectional area and, therefore, double the resistance.  e.g.

8ga   2.061 Ohms/Km
10ga  3.277 Ohms/Km
14ga  8.280 Ohms/Km

Why anyone would want to use 14ga wire on H4 lights (or 9004 lamps) is not
logical, especially if you just paid XXX dollars for said kit to improve
your lighting.  So what if a spool of 10ga costs 2 dollars more than the
14ga.  Run 10ga wire throughout and you will be happy for a long time.  8ga
wire from battery to relay may not be a bad idea especially if you plan on
running 80W/100W bulbs.  We're talking about up to 8 amps of continuous
current draw, you want bigger wires and solid grounds.

Rich Blake