I've been cleaning out my room lately, and in the process I've dug out several cables, both MagSafe and Lightning, in various states of disrepair. I want to plug them into my devices to see if they still work, but I need to know: Is there any risk of seriously damaging them if a cable turns out to be bad?
Yes - lightning carries decent amount of power. Crossed wires could short out a device. MagSafe - worse - more power, less room for error. The only upside there is the MagSafe in side of things is a bit more robust since it handles more power and if you blow the MagSafe on the Mac, it's a relatively inexpensive repair.
Fixing the phone connector would be far more costly.
That being said, the change of damage is low and if you have lots of cables and can make money on them, the risk might be worth it even if you damage things and have repair bills.
I'm reluctant to touch this one with the limited information provided about the extent of damage, i.e. user assumes all risk. That being said the Magsafe cable provides power from an AC source so it is theoretically possible that if there is serious damage to the cable or adaptor that it could lead to a short circuit or power surge. The lightning cable provides data transfer and a lower voltage/power output which is modulated by the separate adaptor, not the cable. One would think there is less chance that the lightning cable would cause electronic damage. Of course if the male lightning connector is physically damaged it could potentially damage the device upon insertion
Again, without the advantage of seeing the cables its hard to get more specific.
Yes, it may be dangerous. Cross wiring may short out your device.