Transfer cash into (or out of) an account for Quicken Classic

I think you're trying to do the transfer incorrectly. In an investment account, you need a transaction of Type=Payment/Deposit. In that transaction you put the name of the account you're transferring to into/out of in either the Transfer field or into the Category field, with the specific syntax of "Transfer:[account name]". A Payment/Deposit transaction is just like a transaction in a banking account, and there is no security involved. In the Security/Payee field, you're entering the name of a Payee, not a security. Here's an example:

Here, I've created a Payee name called "Transfer to Schwab"; it could be anything you want. In the Category field, I've specified this is a transfer from an account called "Vanguard Savings". And this one is a transfer of funds into the account I'm in, because it shows a Cash In amount; transferring to another account would look the same, except there would be a Cash Out amount.