I have a microphone set up just for this for several common mic configurations,. Crambone's procedure is correct.I have a BNC connector set up in parallel to the element in the microphone and introduce the AF signal this way, When the PTT is engaged, you get a proper level AF introduced, Check your mic input in the radio manual. they tell you how to put an AF signal into the radio.
You can make up a mic plug and use the MOX switch on the radio to turn on the Tx. It may be necessary to put a 1 or 10 mF cap in line if there is "phantom" voltage on the audio pin of the mic plug.
However on SSB I use a 1.5 KHz signal rather than a One KHz signal.
An AF signal of 50 mV is typical but your manual may call for a greater signal.
Do you have an Oscilloscope or a Spectrum Analyzer?? I use a SA>
On SSB you should see one peak 1.5 KHz from the center freq on a Spectrum Analyzer.
On AM you should see the carrier and then progressively smaller peaks on each side of carrier at whatever audio freq you inject.You can also see the "deviation" of a FM signal on a spectrum analyzer. If you have a fancy Service Monitor it will give you a number for the deviation.
On an Oscilloscope you will see a modulated "envelope"
How do you plan on sampling the output signal? Are you going to use a load or use an antenna on the radio??
With a Spectrum Analyzer you probably would do fine with a short antenna on the analyzer... With a Scope you probably would do well to wrap a few turns of wire around the radio antenna coax and attach your probe to that. There are "samplers" but that is not necessary to get a pattern.
Giggle scope patterns of SSB and AM to see what you should have on the scope. Here is a start:
https://www.ab4oj.com/test/peptest.html