Needed to replace alternator on a new to me 49. Noticed that there was voltage to engine even when all (at least I think all) battery switches were off and start battery disconnected. The only way to cut off voltage to engine was to disconnect house battery cables from house supply. Does this make sense? Is there a switch I missed? The switches I located were at house battery bank, inverter, panel on starboard settee facing nav station and at start battery. What am I missing? Thanks for the help.
It is not at all uncommon for a performance alternator to be direct wired to the house battery bank. This yields the opptimal charging performance. In the alternator positive cable there should be a fuse within 7" of the house banks positive terminal sized at 150% of the alternators rated output.
Beyond that it is always a good idea to install, in engine bay & clearly labeled an
alternator service disconnect switch. This switch can be de-powered when working on the engine but other than that always remains in the ON position.
A service disconnect switch should de-couple the external regulator at the same time as the alternator output. The reason for this is so that if the switch is forgotten about, and left OFF, the alternators diodes won't be blow running into a zero load situation.