Here's
https://www.extremetacticaldynamics...l-guides/912-full-size-led-light-bar-install/ an EXAMPLE of "stupid instructions".
To power the full-size LED light bar, you will need to locate the unit’s red and black wires. The red wire needs to be connected to the unit’s switch box. The black wire is the negative (ground) wire for the unit, and should wire to the negative battery terminal or a chassis ground. Other wires included with this installation include white, blue, and green. The white wire is used to activate takedown or alley lights. The green wire is used to activate passenger alley lights, and the blue wire activates flashing takedowns.
So, there are white, blue and green. Do you connect them to +12 or ground?
Like I said, the instructions don't tell me what i need to know. e.g Does the RED go to ACC or BATT? Is there any power drain if BATT (on always) is used?
So, as I said "stupid". I made an assumption because this subject has come up before and I have a "little knowledge". Normally +12 is switched and ground can come from anywhere on the body. Vehicles do have specific ground points. Connection to the actual "negative battery" is seldom required. The ground connection is always made. The +12 is connected to a fused source. Whether that fused source can be ON all of the time depends on the design. Some parameter like Quiesent current should be specified.
You really need to ask the manufacturer if they suggest connecting the lights power to a circuit that is on all of the time. The max amount of current the lights draw would also be helpful. All of that changes how you might wire the system. The switch ratings also play a role.
So, I really can;t help you. I can;t even help myself if I was using the info on the light bar I just picked out of my hat.
Need answers to:
1. Can +12 be connected to a circuit that is active all of the time?
2. Quiescent current when no mode is selected.
3. Is the mode selection done by grounding the appropriate mode wire?
4. Recommended fuse size?
5. Does anything bad happen if the mode wire are left open?
I A$$ U ME'ed stuff. Let's say the bar takes 10 amps and I have a 3 Amp switch and you can;t connect direct to the battery. You have to wire it one way. If it can be connected direct to the battery, you can wire it another.