If the problem is there, it might then occur another problem, somehow more erratic but you should check that also. The brown wire (the one that goes to the firewall ballast resistor) goes to a prong that fits the bulkhead connector to the other side (of the wire). The connector has the brown wire just next to the big black wire that goes to the alternator. Now the years and possibly heavy current loads may have that black wire developing huge temps and if it touches the wires next to it, melts them and kind of merges them together so it gets the current from the battery (the black wire has current all the times unless the battery is disconnected). Seems a little complicated, but it's not. If the wires aren't merged, then maybe they are merged (and most possibly) to the inside of the bulkhead connector behind your pedal assembly next to the steering column.