Update

Swapped in the new electronic gizmo. No function of any gauges.

I concentrated on the fuel guage.. confirmed 5 V to guage. Confirmed 5 V to sending unit. Confirmed ground to tank. Tried grounding the guage output, got some needle movement. The needle was off the indications, to the left of E Nd when I grounded the output, it went almost to the E, then returned to the left after I un- grounded it.

On top of that, the first gizmo which I thought I had fried, puts out 5V on the test bench.

I can only suppose that I'll have to order a stock type reducer..

Another look at the stock reducer, and it appears like it would act as a circuit breaker, and reduce voltage as a resistive function.