Can you hear the trim relay clicking when pressing the down button, from either location?
If no clicking from the down relay, then there may be a bad connection, or wire between the relay and two switches.

If there is clicking from relay, then possibly the relay is bad, or the connection on the main relay posts that operate the ptt motor for down motion is bad, not connecting.

For either of these conditions you need to know what wires go where (wiring diagram), and either a jumper wire, to jump over each section of wire from relay back to switch. Or, if checking ptt wires, from relay back to ptt motor.

If control switch and motor switch are acting the same, then it will be one connection (or wire) common to both switches (if not activating/ clicking relay).

you can use a volt meter for testing each section of wire (either continuity, or voltage checks).

Good luck, let us know what you find.