Drove the truck to dinner, when leaving started the truck, glow plugs came on and went to turn it over and everythihg shut down like the battery was dead. While checking battery connections heard a clicking sound in the fuse box. Clicking stopped when I pulled out something that looks to say diode. Noted that the dome light was dimly lite and faded out to nothing. Not sure what the diode does, can it go bad and cause all of the power in the truck to be cut off. Nothing comes on, no headlights, power doors etc. Batteries measure 14,2 when tested.

Any advice?

. Remove and fully charge the batteries--then, you will know if they're good or not. Most auto parts stores will do this for free. Afterwards, clean the battery terminals and cable connections. Ensure all connections are tight.

. Check all under hood and under dash fuses with a test light or multimeter.