Replaced the head lamp bulb but only works on high beam

Are you sure you replaced the right bulbs you may have replaced the high beam bulbs unless you have the type of bulb that has both high and low in one what make and model do you have

Seems like if your other low beam is lit, there's something wrong with the new bulb. Make sure it's the exact type needed, and switch the working bulb from the pass. side to drivers side to check.

Defective headlight relay, Or loose wires going to head lights,

It can be issue with headlight switch,but as its already been replaced.Try disconnecting high beam headlight wiring from headlight assembly and reconnect direct external wire from headlight switch to headlight assembly,then by switch see if headlight is getting off and turning on or not.
See below related help links,similar to your issue.Click the link below:----
Only high beams work but head lights not working on Ford F350?

http://howtobyme.blogspot.com/2011/11/only-high-beams-work-but-head-lights.html

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Only high beams working on GMC Savana?---------- High beams stopped working but headlights still work? http://howtobyme.blogspot.com/2011/11/highbeams-stopped-working-but.html
---------- • Working of Headlight switch? ----------

• Both headlight bulbs blow together? ----------

• Car headlight bulbs don't last long?
------------ Only one head light works on 2001 Dodge Caravan? http://howtobyme.blogspot.com/2011/11/only-one-head-light-works-on-2001-dodge.html

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these will help.
Thanks.

Check the low beem bulbs, they both might be burnt out.

If the high beams work check the bulbs the low beam felament maybe blown
Did they both stop working at same time if so check power at head lamp sw.

sounds like you have a blowen head light bulb. thanks dodge tec

Hello i can assist you open your hood behind the head lamp lenses is a head lamp bulb socket twist it counter clock wise then remove the socket and bulb unplug your old bulb replace with your new bulb and replace the socket back and clock wise tighten.Now turn your head lights on check both high beam and low.

Try replacing bulbs they could have both gone at the same time,I think it takes a 9006 bulb. You could check by pluging low beam plug into high beam bulb if it works the low beam bulbs are gone

could be high/low beam switch