A starter _relay_ will NOT work as a glow plug _relay_. It's grounded through the mounting bolts, so it will be energized whenever the key is in RUN. It's also not rated for continuous contact-closed time, nor is it rated for the amount of current the glow plugs draw. It'll self-destruct promptly.
Starting fluid is dangerous for any diesel engine with glow plugs. If the fluid hits a hot running glow plug while the associated intake valve is open, it can explode out the intake valve, and take out your intake. The fact that yours didn't blow up suggests that the glow plugs still aren't working. Get a new glow plug relay, either a Western Plow relay or a Stancor / White-Rodgers 586-902. If it still won't start on its own, you'll need a voltmeter (aprx. $10) to start testing circuits.