Is there a main fusible link in a 89 model?

Sort of, the fuse box under the hood contains a series of high current fuses
that are effectively the same thing.  The main one is an 80 ampere fuse that
is held in by some 10mm bolts.  It costs about 5 bucks.

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>1)  Are the TPS and Timing related in any way?  Should I do one or the
>other first?

No.  Set the TPS first because otherwise the car might not idle correctly
and then of course setting the timing will be problematic at best.

>2)  How far to the right of the yellow mark is it safe to advance the
>timing?

Don't bother.  The car's ECU has built in spark advance tables that it
employs under normal operation.

>3)  What exactly does that TPS adjustment do?  Is it for performance or
>economy?

The TPS is used mostly to engage the 3k startup when cold, to notify the
computer when the throttle has been released, and depending on how far you
depress the throttle, the sensor will help the ECU decide on how much richer
to makle the mixture for acceleration.