You need to check for power at the YL wire with the key in the START
position NOT THE "ON"
If you do not have power on the YL wire at the starter relay with the key in the "Start" position then you need to check directly at the ignition switch connector.
If you have constant battery power on the BK wire at the starter relay you do not have an issue with Fuses or Fusible Links.
Fusible Links have been used for years, they are all located in the wiring harness coming off the battery + cable.
1990 still used Fusible Links which are a wire placed in the harness and is designed to melt should amperage increase beyond its amperage rating thus protecting the circuit.
The insulation on a fusible link is fireproof so the wire inside melts protecting the circuit with no chance of a fire.
In 1991 Chrysler went to a PDC (Power Distribution Center) on Daytona and LeBaron which replaced all of the Fusible Links with actual Fuses.
I looked at the 1990 Wiring Diagrams Manual and the YL wire does run through a connector before heading out underhood, the connector color is not shown.
It appears to be an 8 pin connector located on a "Pencil Brace at the Left Lower Steering Column.
Besides the factory wiring posted below I am sending you other wiring through PM.
Explaining Fusible Links
Electrical Issues - MiniMopar Resources
1990 AJ 3.0L FSM Ignition Switch/Starter Relay Wiring