2006 Kenworth w900 headlight issue

Sounds like a bad ground on that pigtail or harness to me.

 

I haven't driven a KW since my '95 T800, but the connectors on the headlight harness used to get all effed up down by the hood hinges from road slop and spray. You might try looking down there.

JD

 

The first place I would look is the headlight plug connection from the hood to the chassis for corrosion. I keep a can of electrical terminal cleaner to spray on corrosion spots. I dab some dielectric grease on the connection before I reconnect them. If that isn’t the problem you will have to visually inspect the wire as far as you can for a bare spot or corrosion. If you are electrically inclined use an ohm meter to find it. It is possible to have corrosion inside the insulation without having a bare spot.

 

both high beams on the one side might be burned out.
the low beam headlight has a low light and a high light. high beam might be burned out

 

I've gone through the same thing with my Pete and now my KW.
High beam went out on one side. started chasing wires then remembered, duh. lights burn out!