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Technical Top Tips

Wiring your accessories – tips n’ relays …


If you are a keen off roading 4×4 driver then there’s a good chance you will be wiring up accessories to your truck. Be it high-powered lighting, or a winch to a sound system there are good and bad ways of doing things. Here is a basic guideline to point you in the right direction keeping your work safe and trouble free for future use.



When wiring anything in your vehicle that draws heavy current such as high-powered off-road lights or audio amplifiers, there are a few things to consider. Number one, make sure you use wire that is rated for the amperage that the accessories is going to pull. It is always better to have wire that is ‘over’ rated rather than wire that is not rated high enough. If wire is used that is not rated to handle the current that your accessory will pull, the result could be catastrophic from overheated wires that could melt the insulation or the electrical plugs found throughout your vehicle, causing a short or worse still it could result in a fire. If you know how much current your accessory will draw you can determine what gauge wire is appropriate for your application.
To be on the safe side it is better to use wire that far exceeds the current draw of the accessory. It is overkill but that way there is no question as to whether the wire is rated high enough or not.
If this approach is taken, it is very wise to place a fuse at the battery end as close to the battery as possible. Most wire in a vehicle, if shorted out, will burn before the battery overheats and possibly explodes. If wire that is over rated for vehicle use is used and a short occurs, a short will most likely result in damage to the vehicle of some sorts unless a fuse is put in line as close to the battery as possible. melted-relayWith the fuse there, in the case of a dead short, the fuse will burn out prior to any damage occuring.



Where to Get your Power;
The second important thing to consider when adding accessories is to determine where you will get your power.  Many people will consider tapping into the hot wire of an existing circuit using something called a T-tap or quick slide connector, which are designed specifically for tapping into an existing wire.  This is not always a good idea for several reasons.  First and foremost, tapping into an existing circuit puts additional load on that circuit.  The additional load placed on a circuit or wire may exceed the limits of those wires, connectors and fuse.  Overloading a circuit will do one of two things.  First, it may blow a fuse.  So people will sometimes place a larger fuse in the fuse block to handle the extra load on that circuit.  BAD IDEA!  The fuse may hold but the resulting extra current may be more that the wire is rated for creating heat that can melt wires and connectors and start fires!  The connector to the right was overloaded and fused two adjacent terminals together, causing a short the blew the vehicles main fuse.  Before the fuse blew the connector actually started to burn.  The wire that carried the extra load also had melted its insulation and in places was exposed.  Luckily for the owner of this vehicle, it did not result in a fire but in many cases it does.



A good addition;
With accessories that pull a lot of power it is always better to get your power directly from the batteries positive terminal rather than tapping into the existing fuse block or wiring harness.
In most cases the vehicles existing fuse blocks, wires and connectors are not rated to handle the additional load of high powered accessories such as offroad lights and amplifiers.  If you are the kind of person that likes to add all kind of goodies to your vehicle it might be worth installing an additional fuse block that handles non-critical items like off-road lights, CB radios, power inverters, audio equipment, etc.  This additional block can then be powered by a heavy-duty wire capable of carrying the current required of all the accessories on the block.  Be sure to fuse the block at the battery.
Another important thing to consider is how you control the switching on/off of the power to your accessories.  In almost every case where high current is required, the switch you will use to turn on the power should not handle the load because most switches are not designed to handle higher amps.
The job of switching the power is better left to a relay, so what is a relay?  A relay is a device that, through a magnetic induction coil, turns on the power for you. The switch that is installed in the cab of your 4×4 actually only powers the relay itself which draws very little current. In most  installations a 30 AMP relay will do unless your amperage demands exceed 30 amps.
Another good tip is to use an illuminated switch in the cab to let you know if accessories or lights are in use.




The common method used for wiring lights and other external accessories, for the most part, follows the diagram pictured left.
As in the diagram, a wire is run from a 12 volt power source to the switch in the cab and out to the relay placing a fuse at the source of the power (follow the relay’s wiring plan when connecting wires to the relay).



One of the relays terminals goes to ground. Then run a heavy gauge wire from the battery to the relay placing a 30 Amp fuse in line very close to the battery. Do not connect the power to the battery until all wiring is done. Then run a single heavy gauge wire out to the lights or other accessory. If installing lights, split it into two leads at the lights. If you do this be sure the wire is rated to handle both lights since it will carry the current of both. The diagram shows two leads coming from the relay. Then run the second wire of the lights or other accessory to a good ground on the frame of the vehicle. If the wires will not be soldered together and crimped connectors will be used it’s a good idea to put a dielectric paste on the connectors where they come in contact.  This will prevent corrosion as time passes ensuring a good connection. Then check your work and all wiring before hooking in to the power.
A second wiring option




Text credits; offroaders.com

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