Originally Posted by Landy_Andy
The top one plugs into the UK/Euro trailer socket on the vehicle and has the 'logic' circuit in the plug to convert from separate stop/tail and indicator to the NA combined S/T/T lights. The lower does exactly the same but is plugged directly into the connector on the rear chassis loom (assuming the truck has that connector). If you don't have either of these just get one of these from your local Napa etc... Reese - Taillight Converter
Hope that helps....
Thanks Andy - that helps, sort of. I have the same socket that Lav showed in the original post. It looks like a connector that is simply surrounded by a plastic housing to make a socket that is attached to the bottom of the rear cross member. So, I'm not quite following - but it's my lack of understanding and not your explanation.
I have the top adaptor. Used it once and subsequently lost my brake and reverse lights, but I don't know that those issues are correlated to using the harness. (I didn't notice that I had no brake lights right away; a couple days later, a sheriff's deputy was kind enough to point it out to me over his patrol car loudspeaker. And just discovered that I have no reverse lights this past weekend.) I do know that both the brake and reverse lights were working about a month ago. The harness is just a hunch, thinking maybe I'm using the wrong one.