The red sense wire on my mando 55 amp alternator is drawing 3 amps from my battery wtih the engine not running and with the key turned off. Needless to say, it keeps running my battery down. Does anyone know if the power on this wire is suppose to run through the key switch or if I just have a bad alternator? The alternator feels warm with engine and key off. I replaced regulator and checked diodes but still have 3 amp drain on battery. The alternator does charge just fine with engine running. Thanks...

The wire you are referring to is the excitation lead. The wires are reversed. The excitation lead is, or should be connected through the key switch. The sense lead is direct connected to the battery usually at the starter. The alternator works fine but will run down a battery if connected in reverse.

Thanks for the advice. I checked the only other wire that it could have been crossed with, and sure enough the wire has 12v when the key is on. Tomorrow I will put everything back together and I'm betting switching the 2 wires that have quick disconnects will cure my problem. You have really helped!

I originally mistated my problem.
I have a 3 amp drain on my battery with the ignition key turned off and have traced the drain back to the alternator, however the alternator charges properly. The Mercruiser Mando alternator has 5 wires attached.
Of the 5 wires, 2 are heaver gage and are 12v positive and ground. The 3 other wires are labeled "S", "L2", and "EXC". The "S" wire has 12v when the key is on. The "EXC" wire didn't show any voltage. The wire labeled L2 has 12v on it all the time and is the one that is pulling 3 amps from my battery. I can remove this wire from the alternator and the drain is gone. I tried switching the L2 and S wires and started the engine, but the engine would not turn off. somehow the voltage was backfeeding. Does anyone know what kind of voltage readings I should see on these 3 wires??