Last summer I installed an electric fan in front of the radiator to help cool my Sunbeam in traffic. The original mechanical fan was not able to pull enough air through the radiator to keep the car from boiling over. Perhaps Washington DC in the 21st century is hotter than the Sunbeam engineers thought possible 50 years ago.
Or perhaps it is our traffic. I wrote about the cooling fan in the Overheating post.
I installed the fan using a thermostat switch that turns the fan on when the car’s temperature reaches a certain level. I wired the switch through a fuse and then to the car’s battery. The problem was that the full electrical load of the fan was passing through the switch, which could shorten its useful life. The better approach would be to include an electrical relay.
What is a relay? Simply put, a relay is a high-capacity electrical switch that is turned on and off by a low-capacity electrical current. Relays have two sets of wires, one set to control the relay switch and one to power the high-current device. For the fan, 
the thermostat activates the relay using a low current flow and in turn the relay switches on the high current fan.
In the picture to the right, the four black boxes at the top are relays. The new wiring kit came with three relays, one for the horn and one each for the high- and low-beam headlights. Aside from the starter, which has its own relay device called a solenoid, headlights and horns are the largest users of electricity in simple cars of the 1960s. Interestingly, the original Sunbeam wiring did not utilize any relays. I am hoping that I will now have brighter lights and louder horns.
Sunbeam 