Third Brake Lights

I see most places no longer sell the little black box with wires called "The Logic Circuit". I am in pursuit to install third brake lights on my trailers (if possible depending on the type of trailer) and would like the third (middle) light not to flash with the left or right STT (stop/turn/tail) light. Are they difficult to wire up? What components do I need?

Let me ask one question, before we attempt anything. What trailer connector do you use? I know there are multiple types.

In any event, there are plenty: https://www.google.com/search?client=ubuntu&channel=fs&q=third+brake+light+logic&ie=utf-8&oe=utf-8

Here's a link that might address your issue: https://bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2200674

Edit: Amazon www.amazon.com
118158

Mine only use the 4-wire flat. (white, yellow, green, brown).

Oh, forgot to check eBay. Thanks.