been having problems with my 2000 Seat Cordoba,
First glow light would flash and would not start when this was happening, had to switch on and off until it lit and then went out. now suddenly no glow light at all, changed glow plugs but still not starting.
and not even on a tow.
Find and check the terminal connections on the glow plug relay.
Relay could have failed or burned connections externally or internally.
Operating the ignition (when the relay IS working) you may hear it click on then off several seconds later. It will be a heavy duty special type, not a standard relay.