Here are a few tips about labeling motors and wires on the robot that will make life simpler in the long run, and hopefully avoid some headaches.
Use the extra press-on license plate numbers that one gets when registering a VEX team to label the robot's motors. As shown in the photo below, there is absolutely no question—even amidst the mass of purple stickers—about what motor number is connected which port!
Label the heck out of the robot's wires. A team can often end up dismantling large sections of the robot multiple times over the course of a season to make various improvements and fixes. After putting things back together, there's either a lot of testing required to make sure that each motor is re-connected the right way or, alternately, turning the robot on and having it not work, and then doing a lot of testing to figure out which motors were plugged in the wrong way. Or not plugged in at all, sometimes.
This author's Team 1666 recommends 3M ScotchCode Wire Marker Tape Dispenser. It's got 10 individual rolls of tape (one for each digit, 0 through 9), with a metal toothey-ridge running horizontally across the whole thing (like on a box of saran wrap). Each roll of tape is just a continuous string of the given number: 4 4 4 4 4 4 4 4, vertically along the tape. So students can just peel off a little section, rip it off, wrap it around a wire, and they're done.
This product is expensive for what it is ($37). HOWEVER, the stuff is made to stick to wires, and guess what? It actually sticks to the wires. Team 1666 has tried labeling wires with blue tape “flags” or with label-maker tape, or numbers printed on paper and sandwiched within scotch tape. However, the blue tape was really big, and hard to read, and the other 2 options didn't actually stick to the wires after a short while. As one can see from the photo at left, these labels are quite narrow, don't really get in the way of other stuff, and rather difficult to get off of a wire without a pair of scissors—they can't be pulled off. When they are cut off, they don't leave sticky residue behind. 'Cuz guess what? They're made for labeling wires.
So students should really understand that this $37 item is a valuable resource, not to be used for sticking on each other, or joking around with, etc. $37 for little rolls of stickers is a lot, but they are so useful that Team 1666 chose to go for it, and be judicious in its use.
These stickers also come in flat-sheet versions, which can often be found at hardware stores (and is presumably cheaper without the [refillable] dispenser).
Another option that does readily stick to electrical wire … electrical tape! It has the benefit of coming in many colors, which allows a team to have different colors for, say, chassis motors vs. manipulator motors vs. sensors vs. pneumatics. It does tend to be more bulky than the 3M product, but certainly a lot cheaper, and also available at a local hardware store.
Given the time this author's team has wasted in the past, tracing wires & troubleshooting, we now label each segment of each wire. First, label at the cortex (shown above) so that if the wires get pulled out by accident (god forbid en masse), things can be put back without re-inventing the wheel. Then label each wire on both sides of the junction where the motor controller connects to the motor, and both sides of any extension wire junctures.
Pretty much the second this author's team unplugs a motor from a motor controller, no one can remember if it had been plugged in with matching colors (red wire-to-red wire) or opposite colors (red-to-black). So the team developed a labeling system for that too. When the motor-to-motor controller is connected with opposite colors, as shown in the photo at right, a slash is drawn on the wire label (on both sides of the label, on both sides of the clip), so that whoever is plugging things back together doesn't need to think, worry, or ask about how it should be reassembled.
It's definitely more fun to build & drive robots than to debug wiring problems, so all teams are encouraged to develop a labeling system that works for them. All robots from a school should follow the same set of wiring/labeling protocols, and coaches/mentors need to make sure that all robot teams are implementing that protocol correctly and completely. Universal labeling standards for a multi-robot program has the benefit of students being able to jump in and help each other more readily.