To test for power set your multi meter on DCV. that is the "V" with the two straight lines next it (third setting from the left on the picture provided).
Put one of the probes on a clean metal surface that is part of your car body. This is the earth or negative reference. Put the other probe on the wire you want to test. If there is power there the meter will display 12 Volts or close to it.
To test for a negative or ground (earth) switch the meter to the upside down U, that looks like a horse shoe. Test in the exact same method as above, one probe on the metal body and one on the wire. If it is an earth the meter should read very close to 0 ohms. If it is anymore than a few tenths above 0 then it may be a dirty connection or even a wire coming from a globe. Do not use this wire as an earth.
The RELAY- The standard relay (pictured right, wiring diagram above) is used to turn on high powered devices such as driving lights, air horns and fuel pumps.
Most relays will have the wiring diagram on the side, the one pictured is a regular four terminal relay. there are two terminals for the switch contacts(30 and 87), and two for the coil(86 and 85).
To wire up an after market horn, disconnect your factory horn. Mount your new one and wire it up as follows. Wire terminal 30 to battery + and terminal 87 to the + terminal on the horn.(please note, the pin numbers given are for this relay only, always check that the numbers correspond on your relay) Next wire pin 86 to earth or battery (on this relay the coil must be wired round the right way as it has a protective diode. Its the little triangle pictured on the diagram. the triangle must point to the ve terminal, not the +v).
Driving lights are the same except for PIN 85. Make sure the lights are earthed (some have a wire, others use the mounting bolt) test the back of one of your headlights for a wire that only has power when the high beam is on(this is for spotlights, low wattage 55w or less lights are driving lights and can be wired to the park lights.) Run a wire from the back of the headlight to a seperate mounted toggle switch in the cab. Connect it to one side of the switch (it doesn't matter which side) and run a wire from the other side back to pin 85 on the relay.
Its a simple as that.
According to law, spotlights can only come on when high beam is on, while driving or fog lights (white or yellow, 55w, spread beam, not pencil beam) can come on with any light, low or high beam. Both types of lights must have a seperate switch to turn off the lights at any time.
This should keep the rego man and the police of your back. For any more info on driving lights law, contact your local motor vehicle registry. ENJOY
