Subaru Repair: 1998 Legacy Outback headlights knock sensor, legacy outback, hey jon

Question
I just recently bought a 1998 Legacy Outback with 140k miles from a used car dealership. I know from experience that Subaru's can last well over 200k miles. after driving the car for a while I noticed that every time I touched the brakes the headlightw would get very dim then bright again. at first I thought that it could be that I am not pushing the clutch all the way, but it's not that. then when I was taking a 90 mile trip, half way through, the car started shaking vigorously( I thought I had a flat but checked and I was wrong). shortly after the CE light came on. i finished the trip and had the car scanned. it came up with "knock sensor 1 circuit malfunction". could the knock sensor be to blame for the lights to going dim each time I hit the brakes?

Answer
Hey Jon,

The knock sensor and the head lights going dim are two separate issues.  The knock sensor is the device the engines computer uses to know wether the engine is pinging or not. As far as the dimming, do the lights dim and recover or stay dim? I would suggest having the alternator tested, but not at a parts store.  

Justin