I can't really offer any advice directly to you on this... I'm sorry. I nearly did this with mine once as well. I think unless you can find what trace or component has blown, which can be pretty difficult, you'll need to send it back.
However, for anyone else reading and planning on hard-wiring the Xenarc LCD in...
1) Get a good multimeter. Make sure you're going to wire it up right. IIRC the adaptor is center-positive, but just use the continuity tester on the cig. lighter plug to find out (the top of the plug is positive, the sides are negative).
2) Install a fuse on the positive wire. 3 amp blade fuses seem to be working fine for my 700TSV.
3) If your adaptor plug comes off (like many parts from Radio Shack) for changing out plug sizes, try to tape it down so you don't accidentally put it on wrong should it pop out. (This is what I did. Glad I fused my stuff...)