Not the ABS relay. That is about the same as saying my coffee isn't hot because my toilet seat is up. Wiring harness is unlikely as well - you have mechanical fuel injection (and no spark plugs).
Motor mounts are plausible, but that would just be something that allows the vibration something else causes to be more pronounced.
If you have leaks at the individual fuel lines coming from the delivery valves on the fuel injection pump you could be getting differing fuel pressure to the cylinders. On a five cylinder motor that does not go over well.
Here is a thread worth reading; although, not for the exact same engine.
http://www.peachparts.com/shopforum/diesel-discussion/344531-new-engine-mount-now-engine-rocking-bad-way.html