This is a general installation guide on how to wire a relay harness and switch kit. These instructions apply to any car but for the sake of this guide, we will be using the Ford F-250 as a reference car to wire an LED light bar.
Before we get started, take note of this relay diagram on how to wire up the switch to your LED light. You will notice that the wire has 2 outputs, but for this LED light bar we will only need to use 1 output.
Here is a quick run through of which numbers correspond to which wiring location as well as a video tutorial on the wiring guide. We will be going over each of the numbers on the wiring guide and explain where each of the wires will be tapped to.
#3: Tap to LED light bar positive
#4: Tap to LED light bar negative
#5: Tap to battery positive
#6: Tap to battery negative
#7: Draw to vehicle interior and mount on flat surface
#8: Tap to headlight positive
#9: Tap to headlight negative
Step 1: Gather the shorter section of the output wires (white & black wires) and disable the terminals. You can do this by using some black tape to individually tape each terminal separately so they do not touch. Then cover both terminals together.
Step 2: Now take the other output terminals and tap the white terminal wire to the positive red wire and tap the black terminal wire to the negative black wire. Secure the connections with black tape.
Step 3: From the relay harness, tap the red wire to battery positive and the black wire to ground.
Step 4: Draw the switch portion of the wiring from the passenger side to the driver side.
Step 5: Locate the rubber cover on the driver side and open the firewall cover.
Step 6: Insert the switch from the engine bay into the car interior.
Step 7: Tap the red trigger wire to headlight positive and the black wire to headlight negative. We are tapping these wires to headlight positive/negative so the LED light bar will light up when the headlights are on. This protects from battery drain because when the car is off, the headlights are also automatically turned off. So even if you forgot to turn off the switch the LED bar will turn off along with the headlights.
Step 8: Attach the switch at an appropriate location. Use the double sided tape to secure.
Test to make sure everything works and enjoy your new truck LED lamp.