Over the weekend my buddy and I installed marker lights down the side of the truck along the rockers, and cab lights along the top. I want these lights to only be on when the parking lights are on so I bought a fuse splice and wired it all up and tried several circuits that I thought might work to accomplish this. obviously the first choice was the circuit for the parking lights. Unfortunately this supplied constant power to the lights regardless of the key position or the headlight switch position. I ran into similar issues with other circuits. I currently have them tapped into a circuit that supplies power only when the key is in the on position. does anyone know of a circuit i could use to achieve this or do I need to tap into the power wire for the parking lights?

 

Never wire directly off your lights. You run the risk of burning up all the wires upstream of the oem lights due to the higher electrical demand created from your addons. You need a power relay hooked to the battery and triggered by the parking lamp circuit.

I believe the parking lamp circuit is a brown wire. Just do a google image search for "2004 2008 Ford EVTM" and you should find the proper diagram.

 

from an electrical demand standpoint would it make a difference if I told you that EVERY light in or on the truck is LED except for the headlights which are HID?

 

Have u tried the trailer parking light circuit? I have 3/4" red leds under my tailgate running on that. I just spliced into the trailer harness at the back for power tho, they've worked seemlesly for a or or so

 

LEDs certainly give more light per watt than incandescent, but do you know specifically what the original circuit is rated for? Or how many amps the additional lights would pull? I don't; I haven't taken the time to look up the specs and do the math. HIDs should have their own power source, and they're on different circuits anyway.

As stated, they may cause issues which also means they may not. Still, losing your lights in the middle of the night would not be a good thing. Installing a relay is neither a difficult proposition nor a costly one. It's also the right way to do it IMO. Totally up to you which way you choose though. Lots of people jury-rig stuff and have no issues, but I would never recommend someone to do it due to the potential it may come back and bite me in the ***.

 

Yup

 

Unfortunately it doesn't.

If you think about it from a demand standpoint, if the truck was designed for incadescent bulbs everywhere and you swapped with LED, yes, you give yourself a little capacity back, but that doesn't mean that since you swapped them you should add more.

If you add more lighting, regardless of how the original system was designed, you should be creating a subsystem to power it. You don't want to draw on the original system as any kind of short will cause you headaches.

A relay and a fused +12v line to power it are a cheap power subsystem. It's cheap protection and the smartest way to run anything aftermarket, seriously. If you're not doing this, at the very least, then you're asking for issues.

To your point about the parking lamps, that circuit shouldn't be supplying a constant +12v to my knowledge. It should only supply current when the autolights are activated, or you turn them on specifically, if it's supplying juice with the key off, that's not your parking lamp wire.