Know nothing on Diesel but here are my thoughts. ...
i found that the wire from the glowplug relay to the fuel pump relay only has 12 volts when engine running or when engine cold and ignition on, it shows 1.7v when engine warm/ignition on, the wire from alternator never has battery voltage (which it should have surely??)
This device is mysterious to me, but notice there is a fuse in that relay, guess you already checked it. How this relay receive information on engine temperature, trough the water coolant sensor? Is it working fine? Also, may be the intention is not to have pump on under warm circumstances, have you a pressure leak in the fuel system that may be causing the need to prime the system under warm conditions?
the wire from alternator never has battery voltage (which it should have surely??)
The wire comes from D+ that has voltage only if alternator is working and sending charge. For that, engine should be running.
Drawings for Diesel DDE are here:
http://www.e34.de/tips_tricks/schalt...60_1/index.htm
And for glow plug heater are here:
http://www.e34.de/tips_tricks/schalt...20_0/index.htm
And for alternator here:
http://www.e34.de/tips_tricks/schalt...30_0/index.htm
Just in case anybody want to jump in this issue.
Javier