Where is the "Interior Relay Panel" for an 1989 Cadillac Eldorado? The power trunk will not close and I need to check that fuse.

More then likely the horn relay is stuck closed ,sounding the horns all the time . The horn gets power from the power seats circuit breaker ,no fuse . Relay located in under hood relay center .

Do you know anything about automotive electronic's ? The trunk release is controlled by electronic control modules . Having the vehicle check for DTC'S - diagnostic trouble code's should be the first step in the diagnostic procedure . Then reading how it work's !
Factory service repair info.
Rear Compartment Lid Release System Components
• Body control module (BCM)
• Remote control door lock receiver
• Interior rear compartment lid release switch
• Exterior rear compartment lid release switch
• Rear compartment lid release actuator
• Trunk release relay

Rear Compartment Lid Release Operation
The interior rear compartment lid release switch receives a signal from the driver door switch assembly (DDSA). When the interior rear compartment lid release switch is activated, the signal circuit is pulled to ground. The DDSA interprets this and sends a GMLAN serial data message to the body control module (BCM) requesting the rear compartment lid be released. The BCM responds by applying battery voltage to the trunk release relay control circuit which energizes the TRUNK RELES relay. The trunk release relay is supplied with battery voltage at all times. With the relay coil energized, the relay switch contacts close allowing battery voltage to flow to the rear compartment lid release actuator causing the rear compartment lid to release. The rear compartment lid release actuator is permanently grounded at G402.

The trunk release relay is located in the rear fuse box located under the back seat.

The fuse marked ELC in the trunk fuse block

They are sometimes located in the glove box on the left side or in a console.

I’m happy to help further over the phone at https://www.6ya.com/expert/david_66a56a0239b6ab32

Have you not checked all the vehicles fuses?

You have a trunk release button,wiring to check
for open & ground side & the trunk latch may be
bad after 23 years

There is a block behind the washer bottle on the left under the hood and another block in the trunk on the left side.

loose connection on the big fuses near the battery ,they supply power to teh interior fuse panel

It Could Be The DashBoard Switch Itself Or The Light Sensor which is located Near The Bottom Of Your WindshieldOn the dashboard near your GloveBox may be blocked.There are no fuses for this as it runs directly off your Body Control Module which controls all your dash displays and interior lights.

check 25A fuse in relay center