I have an inexpensive one and just found some pics of it on the internet. The pics show the main unit on the bars and the sensor on the fork. You attach the sensor with zip ties, I prefer to use zip ties with a color color similar to my bike - meaning the silver bike gets the translucent ties and the dark blue bike gets blue or black ties. the re bike, red ties, anyway you get it. for my next computer that I will ount today I will attempt to mount it on the stem. this way I will have more room for my hands and lights. I found a picture of what that looks like too. when wiring you attached the sensor or the mounting bracket on the bars and then loosely wrap the wire any way you want. then attach the remaining end. meaning if you attach the bracket first then you end by mounting the sensor, etc. the other thing you mount is the magnet on the spokes. at least that's how mine works, and it works great. one of these pictures shows that as well. finding the right spoke, the right spot on the spoke and the corresponding spot on the fork takes a little adjusting until you get the sensor as close to the magnet as possible with them tapping each other as the wheel spins. don't worry you can figure all this out - it's not rocket science. :-) I also found a site with the instructions on wheel circumference and it shows the sheet that came with my unit. you asked about wiring and installation not computer factors so i won't get into that.
good luck ith your install! :-)
http://www.foldsoc.co.uk/birdy/sensor.jpg
http://drivemybike.wordpress.com/200...ycle-computer/
http://www.electrical-res.com/cycle-...heel-diameter/
http://farm3.static.flickr.com/2145/...c5481106_b.jpg
this picture shows what the bracket looks like mounting with the unit attached. these slide on and off so you can bring it with you. the skinny thing on the right is for a light