late 99 wont start below 25 degrees

[cowpuncher]

before everyone tells me to check the glowplugs i already did there fine so is the block heater but it wont start untill the temp warms up a little even plugged in. Starter spins fine but the injectors are not fireing no smoke kinda will run on ether but dont like to make it do that and dies when stop spraying it. Local shop i trust has tried to fix it we all think its electrical but dont know what any ideas and open to suggestions. I also put dielectric grease on all connections and all grounds to body that I could find. tryed putting an electric heater under the dash the other morning after 15 minutes it fired right up any body know where I should look and what is the black box that piggybacks the inside fuse box? thanx guys