Begin by exporting the required data from Insightly. Log into your Insightly account, navigate to the specific data module you want to export (such as Contacts, Leads, etc.), and use the export feature to download the data in a CSV format. Ensure you have the necessary permissions to perform this export.

Once you have the CSV file, prepare the data for processing. This may involve cleaning up the data, removing unnecessary columns, or converting it into a format suitable for publishing to Google Pub/Sub. Use a script in Python, Node.js, or a similar programming language to parse the CSV file and prepare the data.

Log in to your Google Cloud Platform account. If you haven't already, create a new project or select an existing project where you intend to set up Google Pub/Sub. Ensure that billing is enabled for your project.

In the Google Cloud Console, navigate to the Pub/Sub section and create a new topic. This topic will serve as the endpoint where your data will be published. Give your topic a descriptive name that aligns with the data you are transferring.

Enable the Pub/Sub API for your project in the Google Cloud Console. Then, create a service account and download the JSON key for authentication. Your script will use this key to authenticate and interact with Google Pub/Sub. Store the JSON key securely on your server or local machine.

Develop a script to read the prepared data and publish it to your Pub/Sub topic. Use a programming language that has a Google Cloud client library, such as Python or Node.js. Use the service account key to authenticate and interact with Pub/Sub. The script should read each data entry from the prepared dataset and publish it as a message to the Pub/Sub topic.

Example in Python:
```python
from google.cloud import pubsub_v1
import json
import csv

# Initialize the Pub/Sub client
publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path('your-project-id', 'your-topic-name')

# Open and read the CSV file
with open('exported_data.csv', 'r') as csvfile:
reader = csv.DictReader(csvfile)
for row in reader:
# Convert row to JSON and publish to Pub/Sub
message_data = json.dumps(row).encode('utf-8')
publisher.publish(topic_path, data=message_data)

print("Data published to Pub/Sub")
```

Once your script is running and publishing messages to Pub/Sub, verify that the data is being received correctly. You can use the Google Cloud Console to view the messages in your Pub/Sub topic and ensure they are formatted as expected. Set up monitoring and logging to track the transfer process and handle any errors or retries as needed.

By following these steps, you can successfully move data from Insightly to Google Pub/Sub without relying on third-party connectors or integrations.