...when changing the battery, you may have damaged or affected one or both of the small red wire connections at the battery Positive terminal. I think you have 2 small red wires there (besides the big one to the starter).

One goes to the 25 amp fuse for the FI ECU (possibly related to the noise you heard?).

The other goes to the small, black plastic junction block nearby, on the inner fender edge. That's the main +12 volt feed to everything other than the starter — including the Warning lights.

I can't explain getting the Orange Arrow light, but I'd take a close look at those smaller wires at the (+) battery terminal — especially since that's where you were working before the trouble occurred.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.