If you are asking about the high beam headlights you either have burned out bulbs or the switch that turns the high beams on has failed. If you are asking about the high beam indicator on the dash I would also think it no longer works account it has failed.
High and low beams have differant filaments. You have to replace the bulbs.
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.
Your computer brain in your truck is messing up take it to a mechanic is my advice. Not sure I even understand what you are asking,but, If its what I think , its just a matter of turning on your lights. For some reason Chevy thought it would be a good idea to have just your low beams and the high beam dash light come on automatically when it got dark, don't ask me why. If this is not it rephrase you question and be more presice.
dimmer switch wore out or you might just have running lights.
Yes
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.
your bulbs are burnt out. when you switch on the high beams its only the high beams. but when you flash your brights it lights up both high and low beams.
These lights have 2 different "lights" in each of them. This occurs frequently. Change out the bulb and everything will be working fine once again.
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 fog lights work with the low beams , they wont come on with the high beams
Have you checked the drl relay?
The low beams and high beams are both H7 bulbs. The fog lights are H3's.