I'm asking this because I have old USB wire and the fixture came with short wires, these wires go from the ballast output to the lamps input on the lamp holders
This fixture is planning to run 7 days a week until the fixture is counted unusable
IDK if this is safe
The wire is about the same diameter as the apple iPhone charger cord

Short answer, no it's not safe, that's only 26 or so gauge wire, if it's even that, it's not rated for the voltage OR current you're going to be driving the tubes at.
You'll more than likely have a fire doing that.

Ok thanks, just wanted to make sure
So what wires will I need to buy

The same gauge that's on the ballast.

Most ballasts these days will have 18 AWG solid leads rated for 600V and at least 90°C.  Pay attention to the details.  You don't want to use speaker wire or lamp cord even if it's the correct gauge.  Larger wire, such as the 14 AWG often found in conduit or Rmoex, would also be safe.  However, most lamp holders are designed to accept 18 AWG, so while you might be able to splice in some larger wire in the middle, don't force a larger wire into a push-in connector intended for a smaller conductor.

Normally single isolated wires, not cable, are used for the internal wiring of luminaires

If the cable is going on the outside of the luminaire, then double isolation is required, if so use wire that matches all the same requirements but in a cable (flex, romex, etc)



Current :

The current of the lamp discharge is between 0.43A for ordinary F40T12 .. 0.8A for HO .. 1.5A for VHO

If the ballast is RS, then also the current of cathode heating goes through the wire. That would be on the order of 1A for lamps up to HO, so then about 2A overall for lamps up to HO

 - #22 and thicker will handle over 2A. However, for Rapid Start you better use something thicker for another reason : The heating supply is only 3.8V and is sensitive to voltage drop. If the wire resistance is too high, it will reduce the heating provided to the lamp and may affect lamp starting and lamp life

 - #24 and thicker will handle over 1A



Voltage :

Continuous - ballast Uoc up to about 500V

Impulse - (if the ballast is of a type using high voltage impulse for ignition, such as Preheat, or at the moment of switch-off of any Magnetic ballast), up to about 1.5kV

 - Most of any random isolated wire will handle 500V when not subjected to mechanical impacts, electrical impulses or so

 - Wires with thicker isolation, such as standard wires for 120..240V use in permanent installations, can handle the voltage reliably enough for permanent application inside a luminaire (since the luminaire body provides additional protection)

 - The wires meant for 120..240V use also can handle the impulses



UV :

Most PVC isolated wires won't last if subjected to UV. If the wires see the lamps, use a protection sleeve over each wire or use wires that are made of something like Silicon + Fiber braid instead of the PVC, or use a sleeve (or heatshrink tube) on the exposed sections of the wires



Heat :

Most PVC wires are 70degC max. If the wire is not going to touch the ballast (you can secure it in the luminaire so), then thats sufficient. If it is going to, then use something for higher temperature. Typical temps of small ballasts are between 90..110deg, large ballasts are cooler



So :

If wiring is in the luminaire and not exposed to UV from lamps and not in contact with ballast, then any ordinary wire meant for permanent installations at 120/240V

If wiring is outside the luminaire, then same but in the form of a cable

If the wiring is exposed to UV or higher heat from the ballast, use Silicon in Glass braided sleeve

Solid or stranded - Most push-in connectors in lamp sockets etc. are meant only for use with solid wire, and it is also more convenient to use on screw connections (no need in lugs). Otherwise use whatever you want