Have you upgraded your earth cable? It helps the starter to get all the power it deserves.
Pictured is the standard Cable and the cable I make to replace it and its plug and play.
Nipple licking is a popular pastime here in Devon . It helps to while away the long dark winter days , until the return of spring when attentions are turned more from nipple licking to the just as popular pastime of bog snorkelling !
I seem to remember that people that had similar problems could slacken the screws holding the the gps and moving it around until the light comes on. It's worth a try.