I retired but I think for these years I used a vacuum gage and checked if I had vacuum to a solenoid valve for the EGR as I found vacuum lines plugged and broken. I then hooked to the hose for the EGR with the engine running at operating temperature. After gunning the engine appx. 2000 RPM this solenoid valve should allow vacuum to the EGR valve. Then I put my finger under the diaphram and made sure it would open with vacuum on it.
If you have an electrical problem I used a logic probe like this.
http://www.autopart.com/tools/toolsmain/tool/T_3031.htm I also have a better quality for pulsing signals.
http://www.ntxtools.com/ sells them Waekon
makes them.
Wiring diagrams
http://www.alldata.com/ sells a years subscription for $29.95.
Well worth the cost if you have problems.