Intermittent total loss of electrical

I was able to get a good look at all the ammeter wiring from under the dash. The splice looks good...
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...and the connectors on the back look original and clean. Could not verify tightness because I could not reach them (only see them), but no reason to suspect they are loose.
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Back to the ignition switch wiring, I found a not-so-great splice into it for the aftermarket tach, and a bunch of loose electrical tape instead of shrink tube and cable ties, so I tidied all of that up.
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Still plan to swap out the switch. I'll do some searching for a suitable fusible link to install at the starter relay. Looking forward to the info on the one you used. Thanks for all your time, suggestions and advice. It is much appreciated!
That's funny you mention aftermarket tach. One of the things I'm doing is rewiring my aftermarket gages and tach to get power from the fusebox.
If the car was optioned with the tachometer in dash, then there was a fuse for it. So I basically copied the factory.

Fusible links.
I bought these 'just in case' needed as replacements or to rework the battery feed.

Top two are from Bill Evans, Evans Wiring.
Blue flag with ring terminal is for a B-body application.
Yellow flag with Packard 56/58 terminal in a connector housing is for A-bodies.
Bottom one speaks for itself.
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Personally I'd be inclined to leave teh starter relay and place the fuse where the splice is. That's just me and mostly because the ring terminals on the starter relay looked OK, so I'd leave them alone. But either way will work fine.

To splice in the A-body one, I'd first try asking Bob if he would sell an male extra connector housing and 2 mating housing for the female terminals.
Then buy the appropriate size Chrysler/Packard 58 style female terminals. For the original wire - that's either 10 or 12 ga.
By 1973 or 74 Chrysler switched to using bullet style connector. Those seem to have more contact surface area. Just mentioning it if your open to not so original looking options.