A rectifier is commonly used on older and smaller outboard motors with lower-amp stators. Its main job is to convert the AC current produced by the flywheel and stator into DC current, which is required for charging the battery.
The rectifier also converts the tach signal from the stator so that the tachometer receives the proper pulse type and can display engine rpm correctly.
There are two very important things to remember with rectifiers. First, never connect the battery cables backwards. Even a brief reversed connection can destroy the rectifier immediately.
Second, never use a maintenance-free battery on an outboard motor equipped with only a rectifier. Those batteries can create excessive voltage draw conditions that may burn the rectifier out.
Because the rectifier is involved in the tach signal, a bad rectifier is often the reason a tachometer is not working correctly. In some cases, simply swapping the two yellow wires with each other can make the tach start working again.
