The most important thing when wiring in a tow harness is tapping into the brake light switch so that the trailer brakes are activated. If you don't have the NAT plug referenced in the link above, you find the brake light switch wire using a test light and splice in there. The rest is running wires from the brake controller to power, ground, and to the 7 pin connector at the hitch.
I have had good success with a basic Tekonsha brake controller unit. Biggest problem is terminals in the 7 way connector rotting out from living in the salt belt, something that shouldn't be an issue for you in CA
Actually they do make a plug and play..(AutoZone) sells them..plugs in, in back of the truck where the tail light harness plugs into the main harness that goes down the fr frame rail...if I remember right it's pretty much below the driverside tail light
Yeah the 4 pin plug is only for lights, does not include brakes (as far as I know). There is a plug and play adapter to connect a 7 way plug to the tail light circuit, but the remaining wires to control brakes have to be run yourself.