I don't have a Palazzo, but our Aria is probably similar enough to give you some hints.
All wiring and plumbing come in to our full wall slide in a single bundle at one point near the middle of the slide. That bundle makes a partial loop under the floor of a cabinet in the slide. The loop opens up or closes as the slide goes in and out. If you can find the correct wires at that point you can test for good power and ground and will then know which direction (back toward the chassis or up into the slide) to trace the wires to find the fault.
On our Aria, it's easy to find where this bundle comes up into the slide by looking at the bottom of the slide on the outside while the slide is extended. There are some rubber flaps that mostly cover a channel in the bottom of the slide at that point.
Edited to add that I had to pull up the floor of the cabinet to get to the wiring/plumbing loop to troubleshoot our awning problem. It wasn't a fun job, but I learned a lot about how our Aria was put together.
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