if the existing harness is in good condition, all you need is to use wiring properly sized for what you add, a good battery, and a good charging system, which might mean that you want to swap your generator to a higher output, or [preferable] go with an alternator

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics