Your post is somewhat confusing. However, I assume it is the 48hp Evinrude battery that is being drained? If so, disconnect the wire(s) from the positive battery terminal and connect a volt meter or amp meter between the positive battery terminal and those wires. A drain would show a reading.
BTW... It would have helped if you stated the year of that engine.
If a reading exists, start disconnecting wires at the engine until the reading vanishes, at which time you've found the culprit.
The problem, unless you've hooked something up wrong is usually a shorted recifier, as follows:
(Small Rectifier Description & Location)
(J. Reeves)
On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.
The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:
One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.
Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue.
