I will check the connectors and the ground connections and see if everything is clean and tight. Am I correct in assuming that the air pump does not turn on if the engine is above a certain temperature?

I do see that there are two changeover valves in the diagram above, If the one in the middle of the diagram allows the engine to be fed air from the air pump, what does the second one at the bottom of the diagram do?

I have assumed that the change over valve which is visible and easily accessible is the one of interest.

 

The change over valve that u can see goes to the rear cross over tube on the plenum for the resonence flap.

The valve u want to test is next to where the oil dipstick tube enters the block. U will have to remove the tb and rear most crossover tube and maybe even the alt to get your hands in there.

 

 

The second changeover valve behind the alternator is the one that opens the secondary air injection shut off valve.
In the above, the most accessible changeover valve right next to the alternator operates the resonator as follows