Hooking up after market stereo?

-My friend is hooking up a after market stereo in his 2003 Dodge ram. He wants to run a 12v wire from his + battery cable into the amplifier. Which is correct. He then also wants to run a second 12v wire from the battery directly into his stereo. Is this correct. Or will something blow out.You can run the head unit's constant power wire directly to the battery, but it's not really necessary. Usually the factory constant power connection in the radio harness has enough current capacity for an after-market head unit, so there's no need to run to the battery. In addition to the extra work involved, small wires at the battery are vulnerable to corrosion. Remember that any wire connected to the battery needs to have a fuse near the battery connection, and the fuse needs to be an appropriate size for the wire. If you use the factory constant power connection in the radio harness, it's already fused in the vehicle fuse box.
There should be a 12v constant from the battery that goes to the stereo and the amp, also a keyed 12v (only 12v when the ignition key is on) that should run to both so the amp and stereo are only on when the key is turned on