There should be no quotation between numeric during the if condition:
{if $productgroup.gid neq 69 or
$productgroup.gid neq 68 or
$productgroup.gid neq 27 or
$productgroup.gid neq 31 or
$productgroup.gid neq 70 or
$productgroup.gid neq 71}
<select name="name" id="name" onchange="plan()">
<option value="1">Car</option>
</select>
{/if}