Posts Tagged ‘hot rod wiring 101’

Hot Rod, Street Rod, Rat Rod, Custom Car Electrical Wiring Made Easy – Part 1: The Relay

Thursday, March 20th, 2014

Hot Rod, Street Rod, Rat Rod, Custom Car Electrical Wiring Made Easy

Part 1: The Relay

Everyone pays loads of attention to paint, tires, wheels, engine, chrome, interiors, but when it comes to wiring your dream machine, there is a hidden monster lurking inside your car. Wiring your hot rod, street rod, rat rod, custom car, or whatever else you would like to call it, does not need to be difficult but does need to be completed correctly. Sure, there are loads of universal wiring kits available that you can order and use. Some of the companies that manufacture universal automotive wiring kits or harnesses are from: Painless Performance, EZ2wire, Rebel Wire, Speedway Motors, American Autowire, and Ron Francis only to name only a few. These universal wiring kits are fine, as they include most of what you need to wire your hot rod. They are simple and safe to use and come with easy to follow instructions. It is so simple that many of these manufactures will label the purpose of each wire. The big problem is if you wish to be a bit different, and wire your hot rod placing, switches, fuse panels, and etc….. in hidden in odd places, then these kits would not work too well. Not to mention, you can buy most of the individual parts to wire your street rod much cheaper than the average universal wiring kit. By wiring your custom car yourself, you can route wires within the car as you see fit. This is what I exactly did on the 1929 Ford roadster hot rod.
This will be the first of many parts on how to wire your hot rod safely yourself, with easy to follow instructions, circuit diagrams, and how to videos. I will even include testing of the various electrical components in the hot rod to determine the correct wire gauge to use and the proper selection of fuses for various circuits. There will even be information on the soldering and crimping of wire terminals, along with how to insulate them and make a professional looking terminal.

Headlight circuit diagram using a relay

A discussion about relays will be a good place to start. The relay is an electrically operated switch that basically has two parts. The first is the electro magnet or coil. The coil when energized from a power source will create a magnetic field. This magnetic field then activates the second part which is a set of switch contacts. Normally when the coil is energized, it will draw a small amount of current. On the other hand, the switch contacts that are controlled by the coil or electro magnet will have a high current rating. For example, many 12v automotive relays will draw somewhere around 0.25amps when energized. Often many of these 12v relays will have contacts rated at 30amps. Relays are often used in the headlight circuits, radiator cooling fan circuit, horns, fog lamps, starters, and many other high current drawing devices. Often when there is an electrical fire in a vehicle, it is due to using switches that have a very low current rating on a circuit having a large current draw, using the incorrect wire gauge, or even with poorly protecting wiring from shorting out when passing harnesses through frames and various body parts. None of this should scare you off. Maybe you already built the high horsepower engine, or produced that high gloss paint finish on you custom car, not to mention all of the welding you did on the frame. All of these didn’t intimidate you, so why not wire your own hot rod?
Below is a video on a basic 12v / 30amp relay and how I tested it, used it to turn a few lights on and off, and a basic circuit diagram of a headlight circuit.