glow plug card question

[GPW661]

Every now and then,,,,,the WAIT light come on like its surpose too..But then its never does all the time...If I work the ingition switch back and fowarth about 20 times..Then the wait light will come on
Can the glow plug card cut in and out ?

 

[AceHigh]

Yes, also the temp sensors could be limiting it coming on, as could dirty contacts and so on.