We're going to go over how to install a basic wired bicycle computer. All you'll need is a third hand cable tightener and a pair of cutters. This particular computer users rubber bands to secure the sensor and the computer head. Many computers use zip ties or a ratcheting mechanism, but they're all pretty much the same principals involved in installing the computer. I'll start off from the fork, going up the fork to the handlebar. I always mount my computer sensor in the front of the fork, that way your normal tire rotation if your spokes do come in contact with the sensor, it will force your sensor out instead of bringing it into the spokes, potentially breaking a spoke or breaking your computer sensor. So with the wire going up, install the sensor. Now the key to having clean lines with the computer wire is keeping everything close and attached to the fork. You'll take your zip tie and attach it around your fork and the computer wire all the way up near the fork crown, and be sure you don't actually get a spoke in your zip tie and keep the head of your zip tie towards the back of the fork. Take your third hand tightener, sinch it, and trim it with your cutters.
Now we will jump from the fork blade to the front brake cable housing, leave a little bit of slack so you don't run the risk of pulling that wire to tight. Now we'll take our head mounting unit and wire, and just wrap that wire tightly around the front brake housing.
Now at the top you want to have enough room to where there's still some slack in the wire before it hits the handlebar. Take another zip tie, tighten it around the wire and your cable housing, again with the third hand tighteners, and your diagonal cutters. Now we'll take our second rubber band and put it around the handlebars, and secure your head mounting unit, and attach your head.
Now with the magnet, just attach it there to the spokes, and you want the magnet to line up with your sensor. Depending on the computer, the sensor needs to be between 1 and 5 millimeters away from the magnet. Look at your computer, move the magnet back and forth across the sensor to see if your computer comes on. If it doesn't come on, you just need to rotate that sensor back a little bit til your at the proper distance without having the magnets hit the sensor. Follow the instruction booklet that came with your computer to program to the correct tire size, time, and day. If you you program the incorrect tire size, the readings on the computer can be miscalculated.