To turn off autocomplete on custom forms you have to add the autocomplete="off" attribute to you <form> tag. Some browsers will ignore this though. A complete breakdown of this attribute can be seen here.

Quick example of code:

<form method="post" autocomplete="on">
<label for="fname">First name:</label>
<input type="text" id="fname" name="fname"><br><br>
<label for="email">Email:</label>
<input type="text" id="email" name="email"><br><br>
<input type="submit">
</form>
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