ABS Light ON and Battery Dead

[dbranc]

Hello out there!
I have a 1988 Mercedes 560 SEL.
The problem I have is that the ABS light comes on. It does it randomly. Sometimes it comes on after starting or after driving for a while. I have checked the OVP relay and the relay located in the ABS module. The only thing I could check with the relay in the ABS module was that the diode was working. The circuit breaker on the OVP relay is good and the relay works with voltage applied to it. I have cleaned the ABS sensors on the left and right wheels. I did not check the one on the rear differential as previous post indicate that the sensor there rarely goes bad.
Recently, the battery has been discharging while the car is parked. Altenator light does not come on while driving and indicator light tests good. The car is not used a lot.
I beleive that the two problems are related. I suspect one of the relays but I am not sure. Any suggestions?