Engine Ping (Spark knock)/ EGR valve

[Dnailer]

Hey guys. Could use some help on this one.
1987 Ram 50 2 wd 2.6l 5 speed.
EGR light has been on in this thing since I bought it and its pinged ever since I bought it so I'm assuming that its related. I replaced the EGR valve and all of the vacuum lines as well as having tried running a higher octane fuel as high as 93. The EGR light is still on and the engine still pings when under a load.
Can somebody help?
Is it related to that little box mounted on the driver's side fender that the largest EGR valve line runs to?

[Dnailer]

Once I move the switch to the other side do I need to flip it back again?
What if the light comes back on?
I haven't flipped the switch yet but I do not think the egr valve is working probably. I checked the timing and it is spot on.
I tried following the chilton manual for checking the egr systems on this truck but it is rather confusing.
Thanks for your help.

[pennyman1]

The light is just a reminder set by mileage, not engine operation like newer cars. Did you clean out the EGR ports in the intake manifold - carbon can build up causing pinging. Also, run a full bottle of redline synthetic fuel system cleaner through the vehicle - its the only cleaner I have used that will decarbonize intake valves and improve power.