could the resistance from hooking an led up to the knock sensor cause any problems?
 

should i wire it in series or parallel?

Don't know...
 

But the Bosch sensors are a dime a dozen in the junkyard. I would get one and play with it first. You have two sensors in any modern audi, so you are probably wasting your time. Get a vag-com and you can log exactly what they are seeing.

FYI ... I didn't know either .. but this was also asked (and answered) in the A4 forum link provided
 

if your interested.<ul><li><a href="https://forums.audiworld.com/a4/msgs/1010715.phtml">https://forums.audiworld.com/a4/msgs/1010715.phtml</a</li></ul>