If you are willing to spend a few bucks and you are not sure your troubleshooting skills are good, find a mobile RV tech. Anywhere from $50 to $150 bucks for the tech to check your work.
Sometimes it is hard to troubleshoot by yourself, I have two helpers that don't question what I ask and do exactly what I want them to do, first is my trusty 12 volt test light and second is my piezo siren, Both helpers have long leads with alligator clips and probes. I can hook them up in locations where I can't see my DMM face but can hear the siren or see the light.
So go to the dump valve, disconnect the wire to the dump valve at the manifold and hook up either helper go back inside turn on the hydraulic system push the button to dump. No light or sound indicates a bad switch or control board. If you are comfortable with verifying the operation of the switch, check for 12v on the line side if there is power to the switch, hook one of your helpers up to the load side of the switch and activate it, once again, no light or sound, bad switch. If there is light or sound, bad PC board.
I am of course assuming you have checked any and all fuses.
I'm not being a joker here or anything dumb like that. If I did those things and any of the steps showed a failure, I'd replace the part that appears to have failed.
Trust your gut.
PS; My DMM leads have pierce points and are threaded and I have threaded alligator clips to use with them so I can work hands free and not have to hold the probes. When I can't see the meter, I use my helpers.
