Connecting to existing wiring.

in my opinion, I cut solder and shrink tube wires that are out in the weather. wire nuts and crimp connector,s will fail in time.

I came across someone that put a light bar on their reverse circuit. He blasted everyone behind him while navigating a dark parking lot. I'm glad he could see because he destroyed my night vision for a good 30 seconds.

I cut, solder, rubber tape, then heat shrink. Shrink the shrink before the 'tape' dries so it gets squished out of the shrink ends. Makes a waterproof connection.

Consider a relay if that lightbar draws a significant load.

Have you checked the trailer connector for a reverse light wire?
I agree that others will not like your light bar install.
Have you tried brighter LED style lamps to improve lighting?

Here is a LINK to a variety of Scotch Brand taps.

I know many, many people don't trust them but if they are so bad, why does 3M sell billions of them every year. And contrary to your belief, ScotchLock connectors are very good. The City of Los Angeles has over 4500 intersections that have traffic signals. The wires are run through underground conduits and the conduits end in surface grade pullboxes. If you lift the loose fitting concrete lids you will find that there are hundreds of thousands of twist on Scotchlocks splicing those wires together. While TS wiring is solid copper and vehicle wiring is generally stranded, they do work extremely well with solid wire.

There are several types of Scotch brand "T" taps and two wire or trailer taps that also sell in the billions every year. Some say that the metal tap you push over the wire will cut the strands, if you use the correct size, there will be little or no damage to the strands.

If you absolutely must have weather resistant connections, there are Scotch connectors for that too. There is no SIMPLE, EASY way of making 100 percent liquid tite connections.

Don't get too worried about the connections and keep them simple.

You might research it more. Maybe it's no big deal and there may already be aftermarket products available for exactly that but some of these lights are computer controlled.

D.E.Bishop wrote:
I know many, many people don't trust them but if they are so bad, why does 3M sell billions of them every year?

Because hundreds of thousands of mechanics, car audio installers, and similar people operate on the theory that TIME IS MONEY. Get the car in and out of the bay as quick as possible, so they can get the NEXT car in. And if the connection fails 3 or 4 years down the road, well, it's not THEIR problem, is it?

D.E.Bishop wrote:
There is no SIMPLE, EASY way of making 100 percent liquid tight connections.

There we are in complete agreement. Soldered connections and ADHESIVE heat shrink tubing is the way to go.

You should have a rather thick gage constant voltage wire to your 7 way connector, if you have one. Good point about the computer monitoring the loads on the lighting circuits, might want to investigate that one.

The "I don't think others would like it" statement is rediculas.
The light bar will ONLY light in reverse. I don't think you will be dropping it in reverse driving down the road.

"I know many, many people don't trust them but if they are so bad, why does 3M sell billions of them every year."

Many many professionals spend a significant amount of time removing those connectors from hatchet jobs. I can't recall know how many of those I have stripped out of the undersides of tow vehicles, fithwheels, travel trailers and class A motorhomes. Perhaps dielectric grease and shrink tubing to weather proof outside wiring. I'm not saying they are junk, just not for me.
I wish i had kept some pictures of the connectors i stripped out.
Keep us posted on your project.

When backing up, turn your headlights off (to marker lights onlyj. You’ll be surprised how much better you can see looking back without your headlights shinging back at you off of things in front of you. You may find no need for reengineering the factory back-up lights.

If I wanted to splice into a wire, I would scrape back the insulation with a knife, wrap the new wire around, solder and tape over it all. No cuts to the factory wire that way.