*I have replaced all glow plugs/controller/temp. sensor/ignition switch and cleaned grounds but very randomly (1 in 20) starts, the glow plugs do not energize. Any thoughts? Broken wire internally?

 

Is it that the Glow Plug Light is not going on or is it actually that the Glow Plug Relay is not working Some Times?

If the Light does not work but you hear the Glow Plug Relay Cick on and if you wait about 30 Seconds the Relay click off; your Relay is working OK and your starts should be normal.

If the Light is off and you don't hear the Relay Click on and later Click off and you have a poor start then it could be the Relay or something related to the Relay; like the Strip Fuse on the Relay is cracked or the Screws on the Strip Fuse are loose.
There is also a Flat Copper Wire that the Screw can be loose on.

Check for loose or missing Nuts on the Glow Plugs themselves.

This is not an endosement to buy Parts there but over on the Dieselgiant Website He has some repair Pictorials. One of them checking the Glow Plugs is listed as Glow Plug Reapair. If you have a Volt/Ohm Meter (Multimeter) it takes about 2 minutes to check the Glow Plugs.
If you go there and go to the page you will need to scrool down the page.

 

thanks bud, the light does not come on and it will not start when it is cold. It happens soo randomly it has been very difficult to troubleshoot. I always think I have fixed the problem. I need to go thru the entire electrical circuit and clean and re-terminate next. BLESS