On your pin type glow plug system, the number one plug is used as the temperature measurement sensor. By monitoring the current in the number ONE plug, the glow plug relay determines when to shut off the light on the dash.
The other suggestions you received were right on. The strip fuse for yours is 80Amps and is located in the glow plug relay unit on the left front fenderwell.
With the pin type glow plug system, replacing all five glow plugs will get you back in business almost every time. Checking them with a meter is almost wasted time. They can check good but still not be doing a very good job.
Good luck and God bless America,