I want to go from the 4 pin standard towing setup on my 98 F150 to a 7 pin setup with an electric brake control unit. I asked a question about this a few weeks ago and got 2 very helpful replies but an still confused. Anyone done this already? I don't want to have to splice into the wiring if I can avoid it. There is a 5 pin receptical just above the driver's right knee but where do I plug the 7 pin receptical at the rear bumper into? Thanks in advance.

 

You could go to Autozone and buy the correct plugs that will let you pull the factory wiring apart and plug in the new plugs that include the seven pin harness.

 

To go from a stock 4 pin to a 7 pin you will need 2 harness kits.

The first is the brake control harness that plugs in to the port in the cab ( you already found that one), and the second one that replaces the 4 pin at the rear end. To locate the connection follow the wires from the existing 4 pin plug toward the front of the cab, they run along the drivers-side frame rail. A few feet in front of the rear bumper is a plug connection (I've seen it wrapped with tape). Unplug the 4 pin tail and plug in the 7-run the wires back the same way.

To make all of this work you may need to add two 30A fuses and 2 relays ; my truck didn't have factory towing, but had the heavy-duty electrical package (whatever that means) so the fuses and relays were in there already. I've seen the brake controll harness for less that $10 (try hitchmen.com) the 4 to 7 pin harness is often sold as a kit that includes the fuses and relays, a fair price is about $50.