battery

[rooster4321]

I have 1975 merc 650 3 cyl, it runs , but if I disconnect the battery cable the motor shuts off . Is this correct? I thought these have a magneto or something to keep it running with the battery disconnected.

 

[merc850]

If you disconnect the battery while the engine is running you can destroy the charging rectifier and/or the switchbox, don't do it! To test the charging system put a voltmeter on the battery terminals and run the engine up to full throttle the VM should go up to 14+ volts; if not then replace the rectifier. They switched to ADI ignition in 1976 which is like a magneto but I still wouldn't disconnect battery while running.

 

[rooster4321]

Thanks merc 850 that's a load off my mind. So the motor will not run when the battery is disconnected. Ok

 

[Texasmark]

The manual agrees with Mr. 850. It says DO NOT disconnect the battery while the engine is running. Hopefully you put your battery lead back on and nothing was damaged. When Merc went to the new 3 cyl loop charged engines they eliminated the belt drive magneto and went to Capacitor Discharge (electronic) Ignition using a CDI module (or function in a common switch box) for each cylinder.

Mark