Military Vehicle Repair: M1009 Glow plug relay, excess fuel, starter button

Question
I have a 1986 M1009. I have converted the starting system to 12V and run it almost entirely on BioDiesel. It runs great with one exception. Occasionally it is hard to start when warm when I am running on pure or nearly pure Bio. I know it is getting fuel because when it finally starts it screams to life until it burns off the excess fuel after which it runs smoothly. On these hard starts I have gone out and cooled the temp sensor with ice or a cold drink (whatever I may have) and it tricks the glow plugs into heating after which the vehicle starts just fine. My question is this. If I were to run a bypass to the 12v terminal and the glow plug supply on the relay and use a starter button to give the plugs a little heat on these hard start occasions would I be hurting anything?? If you had any other thoughts on this I would be interested in hearing them as you have steered me right in the past. Also, what is the small disk sensor mounted in the recess of the filter mounting bracket behind the fuel filter used for? You had me remove mine a few months back for another problem I was having and your solution worked but I have been wondering what that sensor was for.

Answer
The 12 volts wouldn't do anything, since when you have the ignition switch in the run position, there is 12 volts there.
The controller actually completes the ground as needed on the other side.
May be able to ground that with a switch, but i don't know if that would damage the controller or not.