jlinswmo

Hello I recently purchased a 03 F150 extended cab 4WD Heritage Edition it currently has a 4 flat plug. I am mainly wanting to pull my boat to the lake which has a 5 flat. I have a 7 blade to 5 flat adapter I used on my other truck so I was wondering if I could buy a 7 blade RV plug that would plug into my existing harness or what would be the best way to go.
Thank for your help

smokeywren

Hi, jlinswmo, and welcome to F-150forum.com

Your flat-4 plug has wires for trailer lights only. If you plug it into a 5-pin adapter, you'll still have lights only. The 5th pin in a 5-pin plug is for electric brakes on the trailer. But to make the trailer brakes work, you'll have to add a circuit to result in a hot wire going to that 5th pin, and you'll also have to add a trailer brake controller.

More common than the 5-pin plug is the 6-pin plug for a horse trailer. The 6th pin is the 12-volt hot wire to charge the battery in the trailer, or perhaps just the break-away battery on the tongue of the trailer.

7-pin RV plugs add another 6-volt hot wire that's hot only when the tranny is in reverse gear - normally used for backup lights on the trailer.

Anyway, you cannot add just an adapter and expect the functions other than trailer lights to work. You have to do some wiring and add fuses and relays. Easiest way to do that is to buy a 7-pin RV plug kit that's designed to convert the 4-pin flat plug into a 7-pin RV plug. One source is:
http://www.etrailer.com/Custom-Fit-V...id=20031171998

Your dealer's parts department probably also has the kit to convert your OEM 4-pin plug to a 7-pin plug. That kit will include instructions of how to install the various wires, fuses and relays required to do it right. The OEM Ford kit will probably cost you a bit more than the similar kit from eTrailer.com or amazon.com

jlinswmo

Thanks SMOKEYWREN I was afraid I would need to do some extra wiring but thought I may get lucky even if I had to wire I was wondering the best kit to buy
Thanks

Norotso

I'm guessing that your 03 has both the 4 pin and 7 round like mine did. When I had my 03 I had multiple adapters like this for the different trailers I might have to hook up. Throw them under the seat and you always have them.

http://www.etrailer.com/Wiring/Optronics/A75TB.html

tll

If your truck only has the flat 4 you will have to change it to a flat 5. The 5th wire is not for trailer brakes, but for the trailer brake lockout solenoid. It is attached to the backup light wire. This solenoid allows you to backup your trailer without the surge trailer brakes activating. I bet you have disk brakes on your trailer. If the truck has a round 7 pin, you can just purchase the adapter as show in the above post.

seaeagle2

Have you looked real close up under the bumper. I bet in that vintage, there's a wiring harness hanging there somewhere. If not, try tracing the wiring from the 4 pin back, on my 2010, there was a connector where the 4 pin harness plugged into a 7 pin harness. Worst case you could just tap into the reverse wire, that would give you the 5th wire you need.