On the DUAL marine receiver there's just one big wire bundle that you
connect to the back of the radio with a connector. The two power wires
(red and yellow) come with fuses, that are intact.

The second AM/FM receiver I tried is a car stereo (brand new) that has
two connectors: one for speakers and one for power (red and yellow),
ground (black) and power antenna.

I don't know... I have built in numerous car stereos into older cars,
and this is basically the same deal... but somehow I can't get it to
work. I am thinking the radio gods really must hate me or something