how to wire shell?

Picked up a used SnugTop; DCSB, premium back glass, mesh screen sliding windows, folding front window, headliner, looks like reinforced roof; I'm guessing the model is 'Rebel'

I think the guy had it working with third brake,
and dome light, able to turn on even with engine off
I don't recall if key had to be on.

Ideally, dome should come on even with key off, via hot wire to battery.

From my research so far, people typically wire as follows.
Third brake, taps into left tail positive and negative
negative acts as the ground

Dome, people run a hot wire all the way up to the battery, and ground to chassis behind tail

couple things I don't get here.
If negative is the same as ground, why not just "ground" the dome also into the tail?
And, doesn't the tail get constant power?
I thought by law, vehicles are made so their brake lights come on if you press the pedal, even if key is out.
Which would mean constant power supply.

Obviously the easiest part would be adding an in line fuse.



To remove the shell, we simply unplugged from the guy's truck. He had a hole drilled into the plastic side of the bed; behind which I didn't get a chance to see exactly how his wiring is set up.

What I don't get, is why whoever wired it, spliced 4 wires into 3.
I'm assuming they are two pairs of pos/neg, Pair 1 coming from Dome, Pair 2 coming from Third Brake.

Which means previous installed made two wires combine to one, to use something in common. No idea what that would be.
IF positive tail source acts as a signal wire to illuminate third brake,
then probably, the "both" splice is not Positive.
It has to be either ground, or negative.
If it is sharing ground/negative, then maybe an eyelet bolted into the chassis isn't necessary

Maybe I can undo all this shit, peel back the headliner that looks glued on, or unbolt the two lights to see what color wires go to them, to "trace" and know what they are, where they're coming, what they power.

I *did* buy for a few bucks, a 3-way connector pigtail to plug right into this.
But, I can always cut the crap all off, start over, and order to install a 4-way that separates into two paths. One twin wires for the dome, one twin pair for the brake.

Has anyone dealt with this? Getting a shell used that comes with a 3-way?
I'm used to YouTube tutorials showing 4-way.
I think if I read a few more threads, and study a few more videos, I'll figure it out.
I just don't want to wire it wrong because that's how you start fires, melt wires, and blow fuses.
Previous installed even used non-insulated crimps like a Genius,
when heat-shrink adhesive lined crimps are available for like under $1 each...
at least he staggered the 3 crimps positions to not bunch up one section...

Best quote I got was $225 for professional re-install,
but guy didn't really elaborate what it entails, and I (as do you probably) like to actually know what goes into my vehicle.

From other YouTube video's I've seen, it's not really magic.
-wire up electricals
-position the shell evenly around the bed, add a slight flex it can handle if needed
-potentially adjust bed/bolts to center with tailgate
-seal the hell out of it
With sealing probably meaning:
-apply 1" (or similar) foam strip to sides, like what comes with softoppers. Maybe to rear as well
-rear is designed to intake water the most; to reversibly seal that you must take it apart, but waterproof silicone along seams

How to even lift it back up will be fun I'm sure.
Just to get the damn thing on took two people, including me carrying it on my back like a turtle shell and struggling to balance, finding out it feels heavier towards the back glass
vs. a shop that has a forklift...

Maybe the shop is worth it then...Especially if they offer any sort of warranty that stands by their work
I just hope they don't secretly ruin the truck in a way I won't even see,
like gobs of permanent RTV at the front, more hackjob wiring (home depot twist connectors or non-insulated crimps that I can potentially nicen up later)

I mean, if the shell does become waterproof, technically an insulated heat shrink crimp is not needed, nor visible underneath conduit wrap, and works to get the job done/function, but still
heat insulated adhesive crimp being mandatory at certain car brand dealers is kind of the sign of a professional...



I just picked up these:


may order a 4-way if it's needed

 

The stoplight switch at the pedal has constant power. There's no constant power at the back that I'm aware of. Maybe if you dug into the trailer package wiring at the tailgate.

I ran a fused wire from the battery back to the left rear corner for the dome light.

 

Oh. So that probably means if only the stoplight switch has power, that the tail only gets power to illuminate when the pedal is depressed.

AKA Dome wired to that, would only come on if someone is pressing down the brake to activate the circuit
which would make no sense to wire that way
Or, if potentially previous installer had it set up where dome only can come on with key in ignition ON position, which would also be dumb

Sounds like I may need to order a 4-way loop
undo the shenanigans on the shell and start from scratch

and to separate the two pathways
1. Pair One wires, trace/confirm colors from third brake, tap them into tail using adapter
2. Pair Two wires, trace/confirm colors from dome, run power/post to battery (fused) and either tap them into negative on the tail (which technically the old 3-way may be setup/intended to do) or simply find a ground stud behind the tail to put it on with an eyelet and add a nut to retain it

 

For the dome ground I just used a sheet metal screw and eyelet behind the taillight