Yeah, I think the headlight switch changed with the 98.5 update. Mine still has the pull style, and it's a sport truck, without quad headlights.

 

Both of mine are the pull know style. I checked the grounds on bothe trucks and they both seemed good. Just .01 volts less than what the battery was reading.
What seemed like it might not be normal, was that both of the hot wires on both trucks were reading in the 10 volt range, while the batteries were reading 13ish volts. Is that part normal?

 

I wouldn't wonder if that headlight switch is enter self combust mode, pull head light switch check for any melting or misshaped plastic on the switch connector

 

I hope it's not that🤦🏼‍♂️ I just replaced that switch in the 94 about a year and a half ago with the upgraded one from 1 A Auto.

 

If it has been replaced, its probably less likely, though resistance somewhere is causing a drop in voltage, the headlight isolation harness would correct this issue, if its the cause of your root problem, I couldn't say, poor voltage will mess with LEDs though

 

by headlight isolation harness, do you mean a set of relays wired in so that the headlights are getting power directly from the battery, or do you mean a wiring harness these cut off for testing purposes so I could hook uphooe bulbs straight to the battery to test them?

 

The harness removes all current load from the headlight switch circuit, and feed battery power direct to headlights via relays.