1997 Kenworth Led High beam flickering

Define the flickering? Essentially going on and off, or looks like someone jiggling the light as you go down the road?

If the first, check your connections, kws old harnesses are notorious for bleedthrough and inopportune grounding

If the second, fix your hood mounts, steer shocks and maybe replace the housings

 

Drls are not a standard feature that far back, but if they were hacked into say the transmission position switch, maybe that connection is loose/corroded/getting a wiggly signal?

 

Yeah, for DRL lights you need a PWM module on each:
Why do my LED Bulbs Flicker?.

 

Mandatory on vehicles sold or imported into Canada since 1990.

 

I stand corrected

Bleck, when is a 12v system not a 12v system, when someone needs to sell extra things to you