1990 Mercedes Benz 300d Pre Glow Relay switch

Computer problem
1990 Mercedes Benz 300d 4 cyl Two Wheel Drive Automatic

When attempting to start my vehicle, the normal pre-glow light indicator on the dash does not come on as it would normally until the glow plugs reach the desired temperature to start the car. Prior to replacing the part, is there anyway to do an electrical test on it to see if the relay itself is working correctly?