Cabin Fuse Box - 7.5A Tail for powering BD S8 Backlight

Hello - wondering if anyone has insight or experience in doing what I have in mind:

I have a BD S8 40" (white) that is connected to a dual switch (white / amber) that controls the backlight and white light. I plan on getting another BD S8 30" (amber) with the intent of using the same switch to control the amber light. I then plat to use a fuse tap for the amber backlights for both light bars, and tap them into the tail light. Note I plan on using the 64-0122 harness which has four wires:
Red connects to the 12V source
Black connects to the ground
Green is for the backlights
Yellow is for the relay

Question:
1. Is the 7.5A tail light fuse always hot or switched? I'm hoping for a tap that only goes on with the headlamps / parking lights and ideally within the cabin fuse box.

2. Would this wiring diagram work on the switch side:
Dual switch has five wires:
Black for ground; connect to black wire (from the two light bars)
Red for battery; connect to red wire (from the two light bars)
Blue for relay 1 (upper /amber switch); connect to S8 30" (amber) yellow wire
Green for relay 2 (lower / white switch); connect to S8 40" (white) yellow wire
Yellow for switch backlight power; connect an add-a-fuse

The green wires (backlights) for both light bars will be connected to an add-a-fuse and ideally tapped into the tail light fuse.

Note while a switch controller would work better, I don't plan on installing one right now. I also don't have any spare OEM blank slots for more switches. I do want a reversible solution.

Would this work / make sense, and if it doesn't, what's a good alternative?

 

Anyone?

 

Not trying to be a prick, but why don’t you figure out question #1 yourself?
A voltage meter or a test light would answer that question FAST.

Anyhow, to answer question #1.
Yes, it is switched. It comes on with the parking lights.

I haven’t read question #2 thoroughly enough to answer that one.

 

Or posi-taps instead of the harness.

 

Thank you — don’t own a voltmeter to check and too cold outside to work.

No need to use the ground wires for the light bars? I considered posi-taps for the backlight wires but I want something reversible and both wire harnesses are being run to the cabin anyways.

 

The ground wire coming from the light bar harness is meant for the switch. Look at the relay and let us know how many ground wires there are.

 

I meant the ground wires for the switch does not need to be connected? I know to connect the ground terminal coming out of the relay to a proper ground point, of course.

 

Like in the picture I posted, if you want the switch LED to dim with the rest of the dash switches, it needs to be connected to the beige wire.

 

I see, ok. I thought the picture looked familiar and I realize it will function like Kyle’s harness.

Other than that though, does my wiring plan workable? Thanks very much again for your help.

 

Sure.

 

Thanks for reminding me about Kyle’s harness — I’ll message him for a solution.

 

He sells it, I designed it...

 

Tried this based on what I’ve outlined in original post. No luck — the lower switch works and it turns on both the amber and white light bar. The upper switch won’t turn anything on, and seems to just show a white backlight.

Not sure if the switch is the issue now…

 

Post a pic of how you wired it...especially the wires from the relays and switch.

 

Would a diagram work instead? I forgot to take a photo but covering it all up by shrink wrap.

 

Can you describe what the you did with the wires from the lights to the cabin to the switch?

 

I did not do any taps to the cabin wires.

I opened up my harness wiring and found this:

The left cut end is from the 64-0122 harness. The yellow wire is for the relay, but it was connected to the (supposedly) 12V source on the switch, but the switch works as intended.

I wired the new configuration based on this:
coupled 12V black ground —> black ground switch
coupled yellow relay —> red wire on the switch
(amber) red —> blue wire on the switch
(white) red —> green wire on the switch
coupled backlight green wire —> tap to tail fuse

I also tried coupling the two red 12V source from the harness and connecting it to the red wire on the switch, and connect the yellow relay wires to the respective relay wires on the switch but that did not work either. No lights at all.

The amber switch is also white illuminated even with the truck off:

 

The fact that the switch LED's stay ON tells me that the input wire to the switch is incorrect. Juice is entering the LEDS circuit without actuating the switch.
Tell me you understand this drawing:

 

I suspect that the switch was being bypassed last night but I couldn’t think of a way to fix it properly.

From what I can tell with your drawing, the 12V power circuit is closed. The only reason I can think of is due to the coupled wires but I am not sure what else to do.

 

You can test the wanted function by using a jumper wire to the switch connector.