engine bay wireharness

[Wildstreak]

I just got my painless wire kit this week and Im not really sure I want to use it quite yet. I would rather save it for when I upgrade to a electric fan and new autometer gauges which wont be till this coming summer. All I really need is the engine bay wire harness thats comes from the firewall. Everything in the cab work just fine, I really want to get the truck going asap and I was wondering if there is an aftermarket stock engine bay harness that would just clip into the old one or would I have to pick up a used one from here?

any help is appreciated