1985 Chevy Silverado. Truck has 4 headlights. When I pull the headlights on, only one headlight works. Turn on high beams and that light goes out and one on the other side comes on. None of the lights appear burnt out and All fuses are good. Replaced the interior headlight circuit(behind the pull knob) and no change.. any suggestions???

Check your head light bulbs, your truck has the dual filiment headlight bulbs one per side which does both high beam and low beam, 9007 bulbs.
If the low beam filiments are burned out only the high beam will work.
Also look into finding out if the headlight switch is gone bad.
The headlight module and or drl module maybe defective.

The headlight relay provides power to the dimmer relay, then power goes thru a fuse for each light for each circuit (4). The low beam fuses are in fuse block 2. The dimmer relay is controlled by the daytime running light module. The headlight and dimmer switches send signals to the DRL module. You may need a shop manual to troubleshoot the circuits.

If the high beam lights work by pulling on the dimmer switch, you are bypassing the headlight switch.
There should be a circuit breaker inside the headlight switch which could be faulty.

take a look at the dash ground wire located next to the right of ebrake release handle. if the bole holding the ground wire is loose, which was quite common it will cause all kinds of feed back problems, like described in the comments section to your question.

your dimmer switch is at fault. Its location is on the sheering coluum shaft behind the dash in front of the firewall by the brake pedal area

The vehicle should not have to be running for head lights to burn.If high beams work,then the low beam head lights could be burned out,even though they light up with high beams.The dimmer switch,can be the problem if the head lights only work on high beam.

Hi. That sounds like the Low/high beam switch is malfunctioning and in need of replacement. I believe this because the headlights will not come on no matter which power source is attempting to activate them. Clearly, they are not getting power. Since the high-beam indicator light is functioning and indicating HIGH BEAM it IS getting power, There is no further interruptions in that circuit, save the fuse. IF the fuse is good,.. tested good.... Then the switch is bad, if the fuse is bad... replace it. If this doesn't solve the problem You have blown all your headlights simultaneously, or lost all the connectors to the headlights all at once, or possible got so unlucky as to lose all connectivity to just the headlights magically. I'd bet the fuse if I didn't believe that you would have checked that before posting the question here, and that doesn't account for the indicator to be stuck, so.... This pretty much leaves the switch ol buddy, sorry.

Check the fusible links under the hood. Also, double check the bulbs are in fact good. Lastly it could be a defective daytime running light relay.

Headlight switch on dash???

dimmer switch has gone bad need to change your dimmerswitch