RE: Jet Cat help!!
Ted this is very strange. The RPM/EGT sensor cable should not have any influence on the ECU power supply voltage ( unless you have a cable internal damage shortcuting the whole system ).
One thing you could check though: the grounding of the engine connection board. The board is held in position by 3 screws going in 3 aluminium dowels. One of these dowels is metallized on the board.
The lower side of the board will have a metallized strip at this dowel location. Check if this specific dowel is well fastened on both the board side and compressor casing side.
I have seen strange things like that happening with an intermittent connection board mass, including in flight flameouts.