Trailer Brake Wiring

[87BroncoEB]

I have an 87 Bronco with a 302 and I want to put a trailer brake controller on it. I have read in more than one place that the brake light switch will be adversely affected if I splice in at the switch. I noticed there is a 2 blade plug in line with a single wire jumper plugged into it. If i remove the jumper and press on the brake pedal I get juice to one blade and not the other. I suspect that this is the stock "Trailer Brake plug" and that all I need is a pigtail from my local rv shop. The problem is that my local RV shop cant tell me for sure if this is indeed that case. The fact that the jumper is in there makes me ask questions as well. The plug is grey and is next to a brown 5 (or 6 pin, I don't recall) plug that is also empty (Don't know what it is for either). I am not seeing these on any of the simple wiring diagrams in the Haynes or Chilton Manuals.

Help

Tim