Wondering if anyone has any suggestions. New headlights, battery and starter, headlights were all working okay, but I just got it back from having some work done and now passenger side headlights go off completely when I switch to high beams. It's a 69 cutlass 350. Thanks in advance.

 

Check the connection on the dimmer switch.
The switch itself could be bad also.

 

bad bulb[s] is the obvious answer

 

Better yet, check the wiring diagram, where you'll see that there is only ONE wire out of the dimmer switch for ALL the high-beams. That means that even if only one high beam works, the cause CANNOT be the switch or the wiring to it.

Chris is on the right track with bad bulb, but the O.P. said that the bulbs were new. First question is, did you swap the two sides to see if the new bulb really is good? If it is, then the problem is the connector, the ground wire, or a break in one of the wires to the high beam.