Starter stays engaged ONLY in park???

Also, I can't tell what is on the alternator terminal, but it almost looks charred like it shorted at one point. I'm going to buy a new bulkhead connector.
Yes that is the cavity for the R6 line - altehrnator output.
Yes its been heat damaged and the locking tab is no longer holding the female recepticle in place.
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When the multiconnect is snapped into place, its likely the female backs out even more. Result is the metal terminals in that cavity only lightly touch each other. What you may be able to do it push the female from the inside. Its not easy to do because you are pushing on something small that and I think on some of the E bodies the fusebox may be in the way.
There are other work arounds depending on how original you want to preserve things.

This poor connection may explain why the ammeter wasn't reading right.
This is the electical flow for normal starting (non-interlock model).
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Immediately after start, it should be recharging for a minute more.
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But if the R6 feed is not connected well, then the engine is going to run on battery power.


As far as the seatbelt interlock goes, the question remains what was done to return it to normal.
The yellow with tracer was originally S1, and the plain yellow S2B.
S1 and S2 originally joined together at the relay.
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I think what 67Dart273 was trying to get you to do is trace on what connects back to the key switch now.

I don't which S1 or S2 wire will lead directly back to the key switch. But that's what should be connecting to the relay post where there is a big red wire now.
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From your other photo, the big red wire is A1C. That's supposed to be connected to the stud terminal! So here's another reason the ammeter isn't working correctly. Apparently its not connected to the battery.

I don't know what is going on with the washer wire, someone may have been using it as an alternate route to the key switch.
Some wiper switches had an extra terminal for supplying power when the key is in run or accessory. I have no idea if yours does, just a possibility. If so, they could back feed through it.