Hi I have a question I was hoping someone will have an answer for. I recently bought a 20 inch LED to go in the open space behind my license plate holder on my 5.0. It came with a wiring harness and the light works just fine. I hooked it directly to my battery and ran the switch through the fire wall.

My question is: How can I wire it so that it only comes on when the truck is running? The truck is not a daily driver and I feel like the small light on the switch will gradually wear down my battery. I get a little warning about my battery before I turn on my truck.

My battery has multiple points where I can contact the LED wiring kit. Are some of these points only hot when the key is on?

Thanks

 

 

You could wire in a relay that only allows power when key is turned to on position.

 

Don't hook it straight to the battery would be option 1.
After that it will depend on how the harness is designed as to how it hooks up.
There should be a wire form an ignition switched fuse to the light switch (this will only allow it work work when the key is on).
From the light switch it should go to a relay (which is hooked to your battery.
Relay wil be hooked to the light itself.

 

Thanks for all the answers.

Originally when I hooked it up I also didn't think the draw from the light switch would be an issue. It could be that my battery being 6 years old was just on it's last leg and the switch was enough to push it over the edge. It's not a daily driver so it can sit there not started for 3 weeks.

For now I removed the inline fuse which took care of the draw. I also replaced the original battery just today. Replaced it with another Motorcraft battery. Very happy with the performance of the original battery.

The wiring harness that came with light has a relay on it. I just don't know much about wiring.

 

Run the power wire to the switch from an ignition switched circuit in the fuse box in side the cab. This will cause your light bar to only work when the ignition is on. Or if there is a separate wire for the illumination, just run that wire from either ignition switched or dash light circuit. This will let your bar turn on anytime the switch is on, but the light on the switch won't always be on.

Or just disconnect the ground wire from the switch and the light on the switch won't come on, but your light bar will work whenever you flip the switch.

 

Does the switch stay illuminated when you turn it on AND when it is off? If not, you might just be able to reverse the wires.
How many wires come out of the switch? You might just need to re-wire it to make it work.

Otherwise here are some options
1) Replace switch with one that does not light up
2) Replace switch with one that only lights up when it is on
3) wire in a relay for the switch.

These switches are some of the best. They have multiple wiring options to illuminate or not illuminate.
https://www.otrattw.net/