I think it's in the Service Manual. (get yours here.)

 

Gents I have searched high and low cannot find this blue plug. I checked the engine bay fuses and where the 40A trailer fuse should be it’s not there and the pins look to be bare as in there are no fees wires for this circuit. So I’m going to strike it up as I need to hard wire. Unless I’m missing something.

 

What year, model and engine is your truck?

 

1999 Ram 1500 5speed 2wd extended cab short bed

 

Here is the thread I posted when I connected/installed my trailer brake controller. Please note that the plastic 4 pin connector on my truck was white and not blue - https://dodgeforum.com/forum/2nd-gen...he-dash-2.html

 

Just looked for a white one no dice. Knowing my luck I’ll hard wire in the controller and as soon as I finish it up I’ll find it in plain site.

 

That's exactly what I was afraid of, which prompted me to post about the issue and look really hard under my dash to locate that connector. With the help I got from MoparFanatic21 and some persistence, I finally found that pesky connector hiding in plain sight.

Now, If I can just find the factory fog light connector when I get around to changing out my cracked up dash, I'll be extremely happy, as that's likely hiding from me as well.

 

My 2001 2500 was built without the trailer tow package (government issue) but I guess the state/county/municipality added a hitch and three flavors of connections. It did have the four pin plug (hidden very well indeed behind the large wiring bundle at the bulk connector) but the wiring ended at the connector under the cab corner. Had to wire permanent 12V and brake output to the back.

 

If you don't have the trailer package you don't have the plug. To add the controller you need a wire coming from the brake switch then run another wire to the trailer plug in the back. If i remember correctly the controllers wires are, Brake sense, brake, ground and 12v. Look at the documentation that came with the controller.

 

I just did what you are asking about to my 1998 ram with a hitch and 4 prong plug already installed and these items worked perfect. Alot of money and alot of time to install but was worth it.
https://www.etrailer.com/Accessories...ler/ETBC7.html
and item ITEM # 90885. At Etrailer.com