I had a similar problem some time ago on my 90 300E.
After reading mutiple posts regarding the OVP, decided to buy it ($50) - got ready to replace - turned out to be a blown fuse on the original OVP !
I also had ABS warning light on - is yours?
OVP is a small (appr. 25mm x 25mm x70mm) metal box with a plastic top behind the battery under a plastic cover (124, possibly the same on 190). Mine had one fuse on top (10Amp).