Answered: Splicing cables

[ZachDaChampion]

I know that unofficial cables are legal as long as they are identical to official vex ones, but my team does not have a serial y cable for the vex LCD display. If I were to splice a regular vex 3-wire y cable with a standard UART/I2C 4-wire cable, would that be legal to use in competition? I’m mostly asking as the plastic connecters would probably be messed up and there would be heat shrink or electrical tape holding the cable together, making it different than an official cable.

[VEX_GDC]

No, this would not be legal. Rule <R15a> is as follows, with a portion bolded for emphasis:

<R15> Parts may NOT be modified as follows:
a. Motors (including the internal PTC), extension cords, sensors, controllers, battery packs, reservoirs, solenoids, pistons and any other electrical component or pneumatics component of the VEX Robotics Design System may NOT be altered from their original state in ANY way.
i. Internal or external mechanical repairs of VEX Limit and Bumper switches are permitted; using components from these devices in other applications is prohibited
ii. External wires on VEX electrical components may be repaired by soldering, using twist/crimp connectors, electrical tape or shrink tubing such that the original functionality / length is not modified in any way. Wire used in repairs must be identical to VEX wire. Teams may make these repairs at their own risk; incorrect wiring may have undesired results.
iii. Teams may change or replace the gears in the “2-Wire 393” or “2-Wire 269” motors, with the corresponding official VEX Replacement Gears
iv. Teams may cut pneumatic tubing to a desired length

This would be a modification to the original functionality of the cables that you are splicing together, and thus not covered by the exception given in part ii.