VR 200 Watt amp

It would mean that the source feeding the wire isn't switching off as it should.

It could mean that there is a defective transistor but it's not likely to be an FET (mosfet).

Disconnect all speaker wires from the speaker terminals of the amp and disconnect signal cables from the amp. If it powers up, the wiring needs to be checked. If it still shuts down, the amp likely has blown output transistors.

The blue wire from the head unit is the wire that's used to power the remote turn-on terminal of the amp. It should not be connected to the red ignition wire. If the blue wire from the head unit is burned out, you can use the red wire to power the remote turn-on wire of the amp.

If you're new to car audio, you should read through the following site.

BCAE1.COM

Why don't you have the wire that's going to the amp's remote turn-on terminal connected to the blue wire of the head unit instead of the red wire of the head unit. As you have it now, the amp will not go off if you turn the head unit off.

In that case, the circuit feeding the blue wire of the head unit is defective.

Having the remote turn-on of the amp connected to the red wire of the head unit is acceptable.

Using the ignition wire to control the amp will cause the amp to switch off when the ignition is off. There will be no drain unless the amplifier has a defect that's causing it to draw current when it's off.

The red wire feeds the radio. It's not an output from the head unit. There should be a 1 amp (or 1/2 amp) fuse where the remote turn on wire (going to the amp) taps off of the red wire.