After market radio hook up in 73 valiant

A 200W radio is a LOT of power. "If it were" 100% duty cycle, it would be 200 / 12 which is about 16 amps. DOUBLE that if it is 200 per channel.

I would NOT run that off the ignition switch, which is already overloaded. If you have not done the ammeter bypass I would do so, or run a new hot wire (fused) from the battery and if you want the radio on/ off with the key, use a keyed source to trigger a relay and feed the radio

EDIT.......is this the radio?

https://www.dualav.com/support/manuals/dc207bt.pdf

The specifications claim this is only 16 watts