I am putting a set of loghts under the rear bumper to act as utility lights when I'm hooking up my trailer at night, etc. I would like to be able to wire them so that they come on when the back up lights come on, when I unlock or open a door as well. I there an electrical device that functions similiar to a plumbing check valve so that when I turn the lights on in one way, the others don't all come on (ie I put the truck in reverse and these lights and the bu lights come on, but the cargo light, and my step bar lights do not, or the other way around)? Don't know if this device exist, or if my imagination is just working OT.
TIA
DT

 

That does exist, it is a Diode.

Rather than playing games with that, just use 2 relays for the lamps.

In this example, the aux reverse lamps come on any time the truck is in reverse, and the SPDT switch allows for the option to come on with Circuit #53 ( interior lamps ) or to turn them on with any hot ( key position not important ) or Hot in run position ( like an add a fuse in the radio slot ) to turn the lamps on at any time. This added feature is nice for when you have to hook up a trailer in the rain, and don't want to leave the door open. You could always remove the SPDT switch, and just turn on the interior lamps.
If the SPDT has a center off, you can also shut them off of the interior lamps function if you want to.

The reverse vs interior lamps cross over is removed, and another option is added with this diagram. Remove the SPDT switch if you want to use the panel dimmer to turn them on, and shut the door.



There is a how to in the technical articles section on where to find circuit #53 if you need to locate it.
Also the reverse for the trailer tow is in that kick panel, or you can always get that at the rear of the truck.

 

What year is the truck? Put it in your profile &/or signature.

If it already has cargo lamps for the bed (beside the CHMSL), then you can use them to trigger the lights for door open/headlight switch. There's already a diode in that circuit doing exactly what you need done, so I'd just use it.

Then you'd just need another diode for the reverse circuit to trigger the relay for that function, and if the truck has an electrochromic RV mirror, you have a reverse feed in the cab to tap.

Bring all your circuit taps to one relay; add a fuse to bring constant power to the relay; and run the relay's output to your bumper lamps.

 

Might want to check on the diode part.

Not shown in the diagrams for 97, 98, 99, 01, 05, or 06 MY trucks.

The other diodes in the electrical system are shown, but none in the area you noted, just a common splice into the courtesy lamps ( EVTM cell # 89 ).

 

yah ive never heard of a factory diode to prevent certain lights from coming on

 

I don't have a truck courtesy lamp diagram uploaded showing it, but you can see one on p.89-3 (middle section) of this:



It's used in older trucks, like most '80-91 w/courtesy lamps, and some '92-96. That's why I asked what year his truck is.

 

'94 Crown Vics might have used it, but 97 moving forward this is not the case.

I will have to take a look at the 1996 MY EVTM to see if this is still the case, but do not recall that ( also don't recall the Cargo lamps vs interior lamp switch part ).

 

Well, if the OP's truck is an '80-96, he probably already has a diode. When he posts up or fills in his profile, we'll both know.

 

It is not in the 1996 F-150 either




This is a dual switch setup for the warning chime, vs using the Diode.

I can't find the diode in the 1995 CV either, the diagrams changed from what you posted to the LCM type.

Starting to see why I did a universal type install, works over all MY F-150s and CVs for that matter.