This might be something of a project, but probably what I'd do in your place (if you haven't already).

The multimeter I have has an audible beep for continuity tracing. The threshhold conductance it alerts is related to the resistance range setting, so the coil resistance of the sender would provide a beep, if the right range is chosen. You wouldn't need this feature if you could get a helper to watch the meter, but it is really great for tracking down intermittent open circuits without assistance-- you can wiggle things to your heart's content.

But, seems I heard somewhere the insulation fails. I don't know if this is on the silicone wires you replaced or somewhere else. You'd probably have to set the meter on the lowest range to use the opposite mode, detecting a short while wiggling.

If you still have the broken tamper lock for the speedometer plug, you can split a piece of vacuum hose and wedge it behind the side closest to the clock/tach. This might aid the pin tightening you plan for the edge connector.
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Art Benstein near Baltimore