I have an Epipohne G400 and I want to put some Seymour Duncan invaders on it. I took the backplate off of it and the wiring looks really odd. Anybody who has done this before have any tips?
Unsolder your old connections and resolder on the new ones from you new pickups.

If you want to replace all the wiring, go ahead and do it...

One cheap thing you could do is reflow any bad looking solder joints, or clean the components with tha5t no contact spray stuff.
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But, they way the wires come through is like little holes. I'm worried about screwing up my wire.
In my experience of the Epiphone SG's you are going to have trouble getting the wires from the new pickups through the holes from the pickup cavities, into the wiring cavity. It's easy enough to fix either with a long round file, or by re-drilling.

Also the wiring in the Epiphones is pretty crap, as it is with most guitars in that kind of price range.

I'd rip out all the old wiring, pots and switch are replace the lot, using a diagram like this one: http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=2h_2v_2t_3w.
Yeah, thats probably a good idea. I'm kind of redoing my SG. Why spend a 1000 dollars on another guitar when I can mod this one to be just as good. Its just....... wiring isn't my forte. I think I'll take it to a shop..
i think you should post some pictures of it on the thread so we all understand what your talking about