Your high beams work but your low beams do not because the switch is broken that switches between high and low beams. Electrical switches wear out.
The switch assembly is probably worn out and malfunctioning.
Should be like any other vehicle. (pull turn signal stick back (high beams on), pull it back again (high beams off).
To turn on the high beams in a 1970 Chevy C20, locate the floor-mounted dimmer switch, usually situated to the left of the brake pedal. Press the switch down with your foot to activate the high beams. You may need to pull it up to switch back to low beams. Always ensure your headlights are turned on before attempting to switch between high and low beams.
As a guess both low beams are burnt out The daytime running and high beams are the same light filament. Or the fuse or the relay for the low beams.
A 1989 Chevy truck typically uses two leadlights for high beams. Leadlights, or headlights, are usually configured in pairs on vehicles for high beams and low beams. Therefore, it is unlikely that a 1989 Chevy truck would use four leadlights for high beams. It is important to consult the vehicle's manual or a qualified mechanic for accurate information on the specific headlight configuration for that model.
are my low beams supposed be come on also when my high beams are on in my 1994 gmc sierra
None
check the bulb low bean burns out before high beams
pull or push the turn signal lever.
Bad dimmer switch.
just because. how is a rainbow made, why is the grass green we don't know it just is
Headlights have two filaments; one for low beams and one for high beams. There is a good chance that the low beams are burnt out. This doesn't necessarily mean that the high beams won't work. However, it's not too common for both low beams to burn out at the same time. Of course, it could be a fluke. I would replace the headlights with new ones and then go from there.