I own some years an AMC Pacer X .... A great car (you know "Waynes World" ?) , but in my car there's is only a AM-radio.

Here in Old-Europe, esp. in Germany, aren't any broadcasting stations.... But to replace the radio with a new (modern) one ? Nope.

There's a device called "RediRad" you can buy, but ....

So there was the idea: Feeding the music through BlueTooth and then transmit it as AM. 

No modification on the good old radio - only plug a cable in to the antenna connector, pair the device with your smartphone, tune the frequency and listen to the music !!

Inspired from two projects:

1st. bitlunis AM-Transmitter

2ndB.Kainkas AM-Transmitter 

The 1st one outputs (prepared) sound via ESP32's DAC ... But this is only 8-Bit ... Huuuhhh 

The 2nd is more promising: it uses a port-pin as open-drain and voila - you have a modulation.

So I'll do the 2nd ...