The 1984 190D does not have an OVP relay, only '85 and later 190D's have them. Is the glow plug light coming on? It is possible the 80 amp fuse has a hair line crack or one or more of your glow plugs are bad. With the key on (glow position) is there voltage on either side of the 80 amp fuse?

You can test the plugs by taking of the large connector on the relay and measuring the resistance of the glow plugs at the connector. On a cold engine the plugs should read 0.6 ohms. Any glow plug that reads more than 1 ohm is bad.

Chris