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Headlight Relay Wiring
By Adam Sparks
So you want to wire up a relay for your headlights in your CJ. Perhaps you don't know why you'd want one so you're reading this to find out why. Read on.
A relay switch for your headlights acts in a fashion similar to the solenoid on your starter. The solenoid is a switch that is activated by a small electrical current that switches on a bigger electrical current. Rather than drawing all the current that the starter requires through the ignition switch you only draw enough to flip the switch in the solenoid which in turn draws power straight from the battery.
Installing a relay for your headlights does the same thing. It doesn't draw all the power for the headlights through your switch. Instead it only uses the switch to trip the relay and draws power for your headlights directly from the battery. The result is brighter headlights since you're bypassing your headlight switch and smaller gauge wire and drawing more amps right from the battery instead. Since I have IPF H4s, 55/60 Watt, not high wattage, and I wanted the best performance I installed a relay. If you have higher than stock wattage bulbs or aftermarket lamps a relay is a good idea for those cases too to preserve your switch that's 30+ years old or not designed to carry the load you may be asking it to carry.
For the purposes of this installation I installed a Dick Cepek dual relay from Extreme Suspension, http://www.extremesuspensions.com/lighting/lighting_index.htm
First you need to determine which wires come from your high/low beam switch and which one is the high and which is the low beam using your multimeter.
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Then disconnect the battery at the negative terminal.
Wire the high beam side to S1 using a spade connector.
Wire the low beam side to S2 using a spade connector.
Using a loop attach both high beam wires to L1
Using a loop attach both low beam wires to L2
Attach a wire to S3 to the negative side of your battery using at least 12 gauge wire.
Alternatively, ground the relay to a suitable location on the frame or engine.
Attach a wire to B to the positive side of your battery using at least 12 gauge wire.
Alternatively, wire the the power to the charging stud of the alternator.
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Reconnect your negative terminal.
Enjoy your new brighter headlights!
Wiring Diagram
Below you'll find a wiring diagram of how I did this.
Elsewhere on the web see
Daniel Stern Lighting, Why Use a Relay, a much more detailed article than this.