1987 2.5 non turbo idles rough on colder morning's
 

Rough idle at start when abut 55 degrees f or less The car is a 2.5 diesel with only 61,000 miles. It starts easily, it’s just rough for about 3-5 minutes until things get warmed up. The glow plug light does not come on.
I have confirmed it is not the dash light. I cleaned the engine at the car wash and the light worked each time I tried to start the car for the rest of the day. The next day it no longer functioned.
This is what I have checked. All glow plugs show .7 ohms or less. The strip fuse and incoming voltage to the relay both show 12.5 volts. The relay pins only showed 11.5 volts. Should the pins show 12.5 volts? Is this why my dash glow plug light is not working?