Truck turns over and wont start
 

I have replaced gow plug relay module. That didnt work. Wait light comes on for 1 second and goes out and it seems the glow plug relay then short cycles. The truck turns over but acts llike the batteries are dead. I checked batteries, alternator, & starter. Also checked main fuses and all are ok.

I'd replace the entire glow plug system. Most importantly the controller and plugs.

are the plugs themselves good?

turns over but acts like the batteries are dead? sounds like a starter to me!!!

if it is spinning to slow i would also agree the starter is bad, are you in a cold climate? if so then the glow plug controller could be bad, jump the glow plug solenoid and see if it starts. The controller may not be telling the solenoid not to pull in.

I throw a test light on the plugs to make sure they are good. What about your battery cables, worn, corroded cables will cause a slow cranking issue. How old are you batteries and what is the CA rating of them? The batteries in my truck tested good and were 800CA each and I thought the truck started ok. Putting in two new 1000CA batteries made a ton of difference though.

Whats a good set of glow plugs for the 7.3 IDI? looking to get some new ones for my 92 IDI

motorcraft or buer.