Over the years about 99% of the solenoid remote relay power failures I have diagnosed are caused by
The big number one
Sloppy control wire terminations and wire routing
Then
Garbage grade relays (solenoids)
https://www.ebay.com/itm/Blue-Sea-Systems-7700-ML-Series-Remote-Battery-Switch-NEW/163158913491?epid=14018460121&hash=item25fd0771d3%3Ag%3Awv8AAOSwXOVafS3P&_sacat=0&_nkw=blue+sea+systems+battery+switch&_from=R40&rt=nc&LH_TitleDesc=0
Use good wire -- not PVC. Cross link, Hypalon, or EDPM are all good choices.
Use butt connectors and wire terminals that have heat shrink tubing. Buy an assortment found on eBay.
BLACK nylon wire ties outlast natural white about 10 to 1