96 s-10 headlights

I have a 96 s-10 4.3 vortec that has a couple issues.
1: Headlights occasionally switch from the headlights on to the daytime running lights for no reason. Happened twice to me. Luckily I have really bright Fog/driving lights to compensate when they switch. I usually just turn on the parking lights when that happens so it doesn't irritate other drivers with lights flashing every 20 seconds! Any ideas?
Also, I put Sylvania silver star bulbs in my wife's buick & they are great! Do they (or someone else) make that type of "simulated HID" bulbs for my s-10?
Sealed beam, not composite.

2: I have slight pinging on acceleration. I've used premium gas and Lucas fuel system cleaner with no luck. Possible bad knock sensor? I'm not sure where that's located.

Thanks for any help!

John
http://www.automotiveforums.com/vbulletin/images/statusicon/user_offline.gif

I used the power of Google & found out it's probably the headlight relay overheating that's causing my lights to switch. That was in the owner's manual too. (Why would I ever look there?) I can't figure out what could be making it overheat.