Dual battery wiring query

[janul15]

Hello, I have been tinkering with my dual battery wiring on a cruising sailing boat, fitted with a Volvo Penta 2002 diesel engine. Things seem O.K., except for my Makita diesel heater, which won't turn on. One dual core wire leading to the battery has me confused. Sheathed in black, there is a red wire and a black wire coming out of the sheath, both with in-line fuses. I have connected these to the +ve and -ve of number 2 battery, but I'm not sure if these were the original connections. I can attach a picture if it helps.
Regards,
Richard

 

[alldodge]

The prior owner put a fuse on both +and - wires, not needed but won't hurt anything. Could remove the -ve fuse and attach direct

Might think about getting a couple buss bars (+/-) and move all those wires to the buss bars and just 2 wires from Bat to each BB