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You don't even have to select zero span. The function and
purpose of a TG is to output, at all times, whatever frequency
the SA is listening to. As the SA scans, so does the TG.
In all scan modes, the SA should show a horizontal line
at a height determined by the TG's output amplitude.
So just route the TG RF out to the SA RF in. If the trace
rises, you have RF, if it doesn't, you don't, and either
the TG is not outputting or it's off frequency. At narrow
RBW settings, you have to fine-tune the TG to be exactly
on frequency, that's the screwdriver adjustment on the front
panel. Since you don't know that it's spot-on, start with
a wide RBW then narrow it down.

You could also view the TG output on your scope, at low frequencies.
If the SA is on low band, the TG will be between 100kHz and 11MHz.
However, the counter is tapped off at a different point so it's
possible for the TG to output RF without counting, even if the
counter works in EXT mode. Check the condition of A6W1 (Service
Sheet 3) and scope it for RF.

You've received good advice when it comes to checking the
connections; with their inadequate brackets, those
bulkhead-mounted hybrid-D's are notorious
for "signalus interruptus".

A couple of minor corrections to earlier postings:

1. The 8552 47MHz LO is not fixed; it's tuned by the Fine Tuning
control, and swept on spans narrower than 50kHz. The 8443A's
predecessor, the 8601A Option <mumble>, used with the 8553L,
did not input the 47MHz LO. The 8601A generates its marker
with RF blanking.

2. The marker is not necessarily at the SA center frequency,
it can be moved side-to-side with the Marker Position control.

Regards,
Dave Wise