I have a 1980 300td with a WVO conversion. I bought an upgraded 80 amp alternator exactly a year ago and noticed that the battery light is always on. It's very dim sometimes and bright other times. I checked for battery drain by disconnecting the neg terminal and putting a test light between the terminal and cable and there is no draw until I turn on my fuel switch solenoid. So that wouldn't be the draw since it's off when the car is. I checked the glow plug relay with the car off and there is power going to it. There's power on both sides of the large metal fuse and the screw beneath it even when the car is off. Is this normal? I'd think that the power would be off to it when the key is in the off position. Any input would be greatly appreciated.

__________________
Current fleet-
2015 BMW 750i xDrive
2009 BMW 535i xDrive
2004 Chevy Avalanche 4x4
1993 Mercedes 300SD
1993 Mercedes 300SE (parts car)

Previous Benz's-
2001 Mercedes SL500
1983 Mercedes 300SD
1980 Mercedes 300TD
1996 Mercedes E300D
1999 E300DT
1984 300TD-T
1988 Mercedes 560SEL (parts car)
1979 300SD
2003 E500
2004 S430 4Matic
2001 E55
2003 E430