Sorry David........You don't have a high enough security clearance for me to tell you where the switch is to reverse the polarity or turn them off! The reverse polarity is a very nice feature if you ever get to use it! (doubtful)
Looking at the pics when I bought mine it had the same stains of water I just scrubbed it with bleach let it dry good then oiled it back up. Turned out nice.
OUCH! BTW on the 2nd pic I see the harness for the charging system (I think) awful close to the exhaust manifold you may want to secure it lower on the block. Once that plastic wire loom melts then its only a short time before the harness starts melting. Lets call it personal experience on a differe...