Most of the tank harnesses in B747 Classics were crimped connections rather than the current soldered connections. (Of course TWA 800 may have had upgraded wiring installed as a modification) The possibility of arc-over isn't a function of voltage it also depends upon energy. The power applied to the tank units from the FQIS is much too low to supply a spark - the measurement principle is based on capacitance and doesn't require even as much energy as the battery in your watch let alone the 9 volt battery that someone mentioned. If the tank wiring was the source of ignition it would need to have come from an external short circuit. That in turn would have caused FQIS indication problems. Short circuits in wiring usually develop over a period of time and cause intermittent defects for weeks preceding a hard fault. There is nothing in the maintenance history of TWA 800 to suggest such a sequence. Admittedly it's not impossible, merely unlikely. There are plenty of other possible sources of ignition and most of them have now been addressed by a number of ADs and design reviews/changes. We all hope that the potential for a repeat of such a catastrophe has been eliminated, but caution is needed. We still do not know, and never will know, the precise cause of the fuel tank explosion that resulted in the loss of TWA 800.
So carry on surmising and supposing and ooh-ing and ah-ing about the various pet theories, without getting dirty hands or stinking of jet fuel crawling through the confined space of an airliner fuel tank. Searching for corrosion, chafing, lose bits and cracks. Whether you see them or not you're all still relying on the vigilance of the maintenance engineering staff; a much maligned, despised and underpaid group, most of whom nevertheless continue to perform quiet miracles in the background. TWA 800 was lost. I prefer to think of all the piles of quietly rotting aluminium and chafing insulation that, thanks to the efforts of vigilant inspectors, continue to fly safely on their way.
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Through difficulties to the cinema