Actually, marine grade "primary" wire is the best. Each strand is pre-tinned so it will never corrode. Primary wire is limited to about 60V but they do make the equivalent of a marine, pre-tinned, stranded Romex (NM-B) at can be used for 120V AC circuits.
More expensive than standard electrical wire (MT, THHWn or THWN) but IMHO worth the cost. You can buy reasonable lengths on eBay.
Cigar/cigarette lighter sockets and plugs are about the worst tyoe of connectors for 12VDC "appliances". Anderson Power Poles would be 1000 time better !