1993 Ford F-250 Engine won't crank

Electrical problem
1993 Ford F250 Four Wheel Drive Automatic 141000 miles

I have a 7.3L diesel engine. I went out to start my truck this morning and it would not crank. I turned on the headlights and all burned bright. Radio also worked fine. The "idiot" lights on the dash normally all lit up and went off with the exception of the fuel filter light. It remained lit. Just in case, I placed a battery charger on the two batteries (diesel engine) for about four hours. An attempt to crank the motor again failed. I was wondering if this year and model truck had some sort of elecrical circuit tied into the fuel circuit that locks out an engine start upon the actuation of the "fuel filter" light. I would not expect this, but am just checking. Any help would be greatly appreciated.

Thanks!