2006 hhr has all headlights working but one does not workon dim (new bulb).

The other bulb may be bad. Ive seen this on grand ams where we replaced the dim bulb and it was actually the other bulb that was drawing down the circuit. If you had the same problem before you replaced the bulb put the bulb that you removed from the headlight yu thought was bad and install it in the headlight that is working properly. I know it sounds crazy but it will probably work.