2010 Tacoma Rear Passenger Tail Light Issue

Hello all . . . read through these forums a number of times over the years and have save myself time, money, and hassle thanks to the knowledge shared by everyone here, so what better place to ask about a seriously pesky issue I'm having. If I leave out some pertinent/necessary info I apologize in advance, certainly won't be intentional!

My apologies, also, for the length of this post, but I want to be as detailed as possible.

Quick background: I had a cracked lens on my passenger-side tail light for quite a while and had put off replacing it--mostly because I'm frugal and the tail light worked anyway. Got to looking at replacement assemblies and figured I may as well update both taillights. So I ordered some after-market LED models off eBay, about $120 for the pair; main/brake light is LED, the other two have empty bulb receptacles.

Swapped the old bulbs from the old housings into the new ones, install the assemblies, and went on my merry way. Rookie mistake: I didn't verify everything operated as advertised . . . I can only assume they did from the get-go.

We all know what happens when one assumes.

Anyhow, months go by and I think everything is cool until my son tells me my passenger-side brake light doesn't work. I'm a little dubious, but once he steps on the brake for me I can see indeed it doesn't. I have no idea how long it hadn't been working (see rookie mistake above). About a month later we test it again and oddly, it works! WTF?!

First thing I think is 'short'. So, here's the list of knowns:
• Driver-side tail light operates fine, all functions and lights operate as expected
• Parking lights on passenger-side work normally, including LED brake/middle light

I should note here that I got on an LED bulb bender and thought for fun I'd replace the reverse bulbs in the tail lights---I have retained the amber turn signal bulbs, however. It wasn't until I replaced the bulbs for the reverse lights that I noticed he passenger reverse light didn't come on when I put the truck in reverse, so . . .

• swapped the known-good bulb on the drivers-side into the passenger-side ... no workie.
• Placed the (potentially) bad LED bulb in driver-side light to test . . . works fine.
• Replaced/restored driver-side LED bulb and it once again works fine.

So, at this point, I was flummoxed,

I tried the emergency/blinking lights and they worked fine on both sides as well.

So, I know my LED bulbs are good and the parking and emergency lights work fine.

Since I'm no electrician I took the truck into my trusted shop and they test the connectivity and wiring harness---everything checks out fine, no issues anywhere. They tell me they suspect it may be a circuit board in the after-market replacement, say they see it happen all the time.

Okay . . . it was under warranty so I got a replacement from the vendor and installed it last night. I was stoked thinking now I should have functioning brake and reverse lights. You don't reach 53 years of age without a healthy dose of skepticism and wariness . . .

• Installed the new assembly, turned on the parking lights . . . top and middle (LED) lights come one---this is a good start.
• Put the truck in reverse and BAM! I had a reverse light on the passenger side. Nice!
• Tapped on the brake, but no red light from the passenger side . . . *sigh*
• Try the reverse again for shits and giggles . . . now it doesn't light.What ??
• Like an idiot I try it again, of course it doesn't work again.Don't mock me, everyone pushes the elevator button again when it doesn't seem to respond right away.
• Undo the power harness/plug the reattach (yes, with power off) to make sure the connection is good. Still no reverse light or brake light . . . but again, the parking light works fine yet the brake does not . . . only on the passenger side.

As if that weren't enough, When I fired her up this morning and put her in reverse the passenger-side light came on! I backed out, put on the emergency brake (leaving it in reverse) then walked back to make sure I was seeing correctly . . . sure enough, the passenger-side reverse light works now.

Got to work and had a guy step on the brake for me, thinking maybe my karma was on the upswing. Nope, brake light still doesn't work.

Sooooooo, if you read this far, here is my question: I have replaced the (theoretically) bad first after-market tail light assembly, yet initially had the same issue which seems, in part, to have resolved itself?? But . . . I still have no passenger-side brake light function, yet that same LED comes on for parking lights and emergency lights.

If, in fact, the harness and wiring are good, and . .
If, in fact, the assembly in question is actually good (given that the LED works I'm willing to make that assumption) . . .
What would cause the brake light function not to work? Is there a bad switch somewhere?

Any insights are greatly appreciated! I'd like to avoid another trip to the shop if it's something I can readily fix or replace myself.