Have a 1989 7.3 diesel new glow plugs ,power to glow plugs new batteries 650 crankiing only. if I have truck plugged in (block heater) turn key on and wait for start light to go off truck will start great .if not plugged in it will not start temps are in the low 60s I wouldn't think it would need
plugged in to start at those temps any thoughts are appreciated thanks

 

Have you tested the glow plug relay and controller?

 

Not sure how to do that for sure just know that it is getting decent voltage to glow plugs

 

Glow plug thread is here:https://www.ford-trucks.com/forums/9...le-system.html
Read it to trouble shoot the system.

You say new glow plugs, what brand?
The consensus is most glow plugs are crap except Motorcraft/Beru. A few people have had success with other brands, but mostly failures.

 

and how long is the glow plug light staying on? it if is only throwing power to the glow plugs for 1-2 seconds, that is not good enough to do anything. you need at least 10 seconds of wait to start light/power to the glow plugs for them to heat up.