You can splice them in...but it's easier just to swap out the whole dash harness. You'll have to pull the tweeter covers off, pull the fuel/temp gauges out, unplug the dash harness at the fuse box by the driver's feet, unplug the roof/cruise/dimmer controls, and unplug the dash harness up under the dash on the passenger side. You can see where it plugs in when you get the passenger tweeter off. The new dash harness will swap right out for the old dash harness. On the passenger side plugs, you'll have one extra plug that you don't need, but you'll need to ground the black wire from it, or else your turn signals will flash (on the gauges) like they're on hazard mode. They will work from the outside. Make sure you ground this wire in a good spot, because if you don't, you can fry the dimmer module. BTW, did you get the dimmer module with your dash harness? If not, your gauges will be on full blast...the old dimmer module won't work with the EL gauges.
Mine...
Before:
Inbetween (it's not as bad as it looks. I just work messily.):
After: