How can I tell if my truck has the plug for electric brakes?

 

Do you mean the barke controller connection? If so look under the dash on the driver side, there will be large connector (mine was blue colored). Make sure you have the correct adapter for your controller. I got my adapter at Camping World for $16.

http://www.tekonsha.com/bch3020.html

 

If you have the trailer package then you have the controller connector.