I made a headlight harness for the Miata tonight. Well, I have a few wires left to patch in, but it's 90% done. The battery puts out 14.9 V at idle, and I was only getting 14.0 V at the headlamp
So I should see nearly a whole volt of increase when it's all said and done. Overall, it wasn't too hard. The battery is in the trunk, so that made things a little interesting, but running the wire was still very easy. I'm using 12-gauge stranded wire for everything, except for the trigger wires I'm using the OEM harness (which is quite thick surprisingly). The only odd thing, which I discovered upon metering things, is that this car uses a ground-switched electrical system. I work with low-voltage for a living, and I cannot understand the purpose of ground-switched systems. Anyway, I'll report back in a few days once things are all done.