Newbie questions on trailer plugs -

My 2002 F-250 has 3. I find that a bit strange? One is in the bed, on the left side, at the tail light, near the top of the bed rail. I saw a thread where someone referenced a "bed wall socket" for use with a fifth wheel. Is it safe to assume that is what this connection is? I do not have a fifth wheel and there is a bedliner in the truck so I am not able to determine if there was one.

Below the back bumper, near the hitch are two connectors. One has 4 pins, stacked vertically. I am led to believe the 4 pins are GND, Tail lights, RT Turn and Left Turn.

Next to this connector is another one that has a cover held closed by a spring. This connector takes a plug. I have not looked at/studied it to say what kind of plug it accepts.

MY QUESTION IS -

Like with 110 v residential wiring, is there a tool/device that one may plug into these connectors which, by means of lights check the wiring and tell you if it is wired correctly. Such as this:

 

They do. Here's one for a 7 -way plug.


Rv's usually use the 7-way plug.

Horse trailers and equipment trailers usually use a 6-way plug

Small utility trailers with no brakes usually use the 4-way plug

They do make a 5-way plug also but you don't see that very often.

You will have to buy the tester to fit the plug you want to test.

 

Thanks for that link. Found it interesting and helpful. It also led me to this -

4-pin Tester