On the floppy disk drive, the 34 edge board connector terminals are identified somewhat differently than in most applications I have seen which use flat cable;
| <- cut in circuit board
1 3 5 7 9 .... 33
2 4 6 8 10 ... 34
Thus, all of the odd numbered terminals are on one side and all of the even are on the other. Note that in interfacing, we are primarily interested in the even numbered terminals (ground appears on all of the odd).
A cut in the circuit board to permit keying with the cable assembly identifies the low numbered terminals and in placing the cable on this connector, the conductor which is distinctively colored is aligned to be on the side of the cut. In the disk drive I have here on the desk, terminals 2 and 34 are also labeled. If all else fails in locating terminal 1, find the arrow on the plastic cable connector. This is terminal 1.
If you have a cable that is 34 pin edge board on one side and two parallel rows of holes on 0.1 inch spacing on the side that would normally connect to the controller card in the PC, you might consider simply inserting wires into the holes. Note that terminal 1 is marked with an arrow on the plastic connector, and following the above, terminal 2 is across from terminal 1.
However, if the other end of your cable is terminated in another edge board connector, you may wish to cut the cable and solder your leads directly to the proper conductor.
In doing so, it is very important that you understand that the distinctively colored conductor is NOT terminal 1. Rather, it is the terminal across from terminal 1, in this case, terminal 2. Thus, as one proceeds across the cable from the distinctive stripe, the numbering is;
2 1 4 3 6 5 8 7 ...... 34 33
Optical Sensors.
In all of the junk disk drives I have disassembled, I have found two pairs of optical sensors; one to detect the "write protect" on the disk, and the other to sense the alignment hole. Each pair consists of an LED and a photo transistor. I have not made any attempt to determine how to tell them apart or how to determine which leads are which.