The SILVER relay is the one that connects the chassis and coach batteries together to charge the coach batteries off of the engine alternator, and using the boost switch, allows you to "jump start" the engine using the coach batteries.
Those relays are notorious for failure. They will click or clunk but not make contact, as the contacts are burned up. The relay is only rated at 80 amps, its junk, very common failure item.
You should replace it with a Cole-Hersee 24213 which is continuous duty rated at 200 amps and has tungsten silver plated contacts.
Amazon - Cole Hersee 24213 relay, $50
This relay is physically the same size and mounting as the existing one. It has TWO small terminals and you have to fabricate a small 14 or 16 gauge wire that connects one (either one) of the two small terminals to the mounting bolt to provide a ground for the coil. The large terminals are slightly shorter and the nut will end up flush with the end of the terminal stud, but it works. Very common replacement.