Example of a generic client site GTM HTML Tag to collect custom events

gistfile1.js

// This is intended as an example, please don't assume it works or judge my hackery style
// This would be wrapped in a script tag in GTM and make sure jQuery is present, you could
// use vanilla Javascript if you please.

// Place our generic function
function simoPush(c,a,l,v) {
  dataLayer.push({'event' : 'GAEvent','eventCategory':c,'eventAction':a,'eventLabel':l,'eventValue':v});
}

// Now add in your client side events to measure

// Form submits
$('form').on('submit',function(){
  simoPush( 'Forms', 'Submit', $(this).attr('id'), window.location.pathname);
  return true;
});

// External link clicks
$('a[rel="external"').on('click',function(){
  simoPush( 'External Links', 'Click', $(this).attr('href'), window.location.pathname);
  return true;
});

// Youtube plays with embeds set as enablejsapi=1
function simoTrackYT(e) {
    if( e.data == YT.PlayerState.PLAYING ) {
      var vid_url = e.target.getVideoUrl();
      simoPush( 'Videos', 'Play', vid_url);
    }
  }
}
function onYouTubeIframeAPIReady() {
  var player = new YT.Player('player', {
    events: {'onStateChange':simoTrackYT}
  });
}
$('form').on('submit',function(){
  return true;
});