I used a one wire that only had one wire
Usually the problem with the one wire is that the older cars run the voltage thru the entire system,rather than relays like the newer cars.You can either hook the one wire straight to the battery or hook it into the horn relay buss to power up the internal components better.The best thing is to take the load off the wires under the dash by doing like Dave has done and use relays on the head lights etc........this takes the load off the underdash wires and cures the voltage drop from the power snaking thru 20 foot of wire and 3 switches Relays take a wire that used to run full voltage and amps and converts it to a remote wire for the relay which draws mili amps compared to full amps thru the switches.
The more relays you can install under the hood to keep the load from traveling thru the underdash wires the better........and use some sort of fuse on everything,I am not too hip on the fusable links or better stated too light of a wire to burn in two sumtin about glowing red wire melting in two has no appeal to me