Not knowing all the checks that have been done I can only suggest something basic. On mine the brake has to be set and the engine running when operating the slides. If you have the key turned to accessory and the engine not running your battery may not be able to handle the load of the slide. I am probably way off but all I can suggest; Sorry.
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Robin, Carolyn and Maggie the Schnauzer - 2015 Winnebago 30T, towing 2002 Jeep TJ