If you happen to have any 12V bulb/socket with a pair of wires coming out of it (pigtails) laying around, just bare the insulation off of each of the two ends & ground one end to bare metal on the firewall and wrap the other bare wire around a thin metal probe & stick it in the bulkhead terminal where the main power lead goes in (trace the power from the batt positive lead to the starter relay & it continues on to the bulkhead to that particular terminal). if no light then the FL has popped, if it lights then the open is under the dash (the 2 bulkhead halves coulda lost continuity in that particular male/female brass terminal connection between the two bulkhead halves there on the eng side of the firewall but not likely). if it is the FL then NAPA has a replacement for cheap & I would have someone crimp/solder it in being carefull to wick away the heat from the soldering iron in the process. If the open is under the dash then start with the ammeter terminals as mentioned. keep us updated. EDIT batt neg cable connection to block coulda lost its connection/continuity which would render the system dead like it is but I would not expect a "pop" from that potential.