Sounds like you need to do some work to weatherproof your fan relays and wiring. Maybe something like this would help. I don't know if this specific relay has an adequate amperage rating for your application.
https://www.summitracing.com/parts/p...SABEgIyYvD_BwE
If your distributor power wire voltage is jumping around again, then this is an opportunity to do some investigating. Is your distributor power wire spliced into the harness at the ignition switch? See if the voltage is jumping around where it ties in too. Hopefully you will find a flaky connection that needs to be redone.