The ABS light in my 1988 740 Turbo is on. Most of the time it's on as soon as I start the car, once in a while it comes on as soon as the car rolls forward. I checked the resistance at the connectors near the struts for the front sensors and both are within spec. I checked the fuses, and I checked that the antisurge relay terminal 3 gets the supply voltage when the car is running (and 0 when it isn't) - although the voltage seems to only be 1.6V instead of 12 (both supply and terminal 3). The Haynes manual mentions a converter next to the ABS module that's supposed to have 12V at all terminals, the only thing I see is a black box attached to the module - is that it? How is it detached from the module? And is there a way to directly check the relays on the hydraulic unit in the engine compartment? Would dirty sensors cause the light to turn on before the car moves at all? Any advice would be great, I'm trying to avoid random parts swaps to get this fixed.

Zack
1980 245DL M46 291k
1988 745T+ M46 234k