Squadron 24v Light Circuit Issue

Trying to help a friend- he has a Fairline squadron 55 - none of his ceiling lights work- pulled the panel and there are two large DIN connectors on the top rail- one derives power from the 24volt switch on the panel which is working fine- this then goes on to various 24V circuits that all work fine-- the second of these DIN connectors supply seems to come up thru the deck at the back of the panel- we are getting no voltage on this cable. If i jumper from the switched cable over to the second, his lights work- Is there a disconnect, a fuse, a breaker somewhere that controls this second cable-? Both supply cables appear to be pretty large- about 4gauge wire. I have looked in the engine room, the battery compartment, behind the panel, under the dash etc but have not found anything-- got to be something simple i am missing. My friewnd is a disabled

have not contacted Fairline- if you have a contact number it would be appreciated-- i have looked through the wiring diagrams that came with the boat- they are quite extensive but do not address where this cable goes or is routed-- they show a 24 volt power source cable running to the batteries which i believe is the cable that has power. The 24 volt light duty circuits have a diagram but unfortunately it ends at the panel. right now i am leaning toward the possibility that this cable i am questioning runs back to the batteries on the same run that the other 24 volt cable runs, going to a circuit breaker labeled domestic which is on the forward bulkhead of the battery compartment-- to get at the back of it requires going over the top of the generator in the engine room and removing a cover with about a dozen screws that is over the connections- that is probably what i will attempt tomorrow.