Volkswagen Repair: 1979 Beetle EGR light on, vacuum leak, throttle valve

Question
I am currently working on a 1979 Volks. Beetle and the EGR light is on. I cannot find any information on how to check and see what is wrong. Could be many things. Where should I start and what are some common problems that set off the light?

Answer
Jay,
 Depends if you have a mechanical or electro/vacuum EGR.  With the mechanical, the linkage (rod) to the throttle valve may be out of adjustment.  On the electro/vacuum style, there may be a vacuum leak, or the throttle valve switch is bad or misadjusted.  Another possibility in either case, the EGR valve or the pipe may be clogged.  

Rick