Brights only

I’ve replaced the relay and bulbs for my '92 Rodeo but only the brights work when I pull my dimmer switch. How do I fix this and what is the cause of this??

Perhaps the low filaments are burned out on both bulbs?

If the bulbs have been replaced then the dimmer switch could be faulty. I would check the system with a voltmeter before replacing the switch. You could have bad connections as well.

Sorry missed the changed the bulbs part.