7 Prong Wiring. I'm not too keen on trying to run wires from the battery back to the back of the truck unless necessary. Please feel free to give it a go yourself and I hope you enjoy.
OPT7 7-Pin to 4 Way Adapter Tow Hitch Flat Blade Trailer ... (Virginia Rodriquez) You can use the wiring from the four prong (blade) outlet. Old ignition had three connections: -IGN -ST -BAT. Please feel free to give it a go yourself and I hope you enjoy.
The older, outlets are Your three-prong cord will not have a green ground wire.
In place of that wire a ground strap or short. Wire Work Prong Setting. by Rhonda Grandee. Actually, it would be better and safer (and cheaper) to change the dryer cord to four blade.