I have a 1987 Ford F250 Deisel...the glow plugs will not come on..the truck will start if you use either

 

Have you tested the GPs for serviceability..ie do they work and what brand are they.

 

Test the glow plugs, using the test lite or meter method. You will find posts on this. You should pull one and find out what brand. If it not beru I would suggest replacing them all with beru.

 

Does your glow plug light not come on? Is that what you mean?
It is most likely your GPs as the others have said. It might be the controller. Easy to check the GPs. Tricky to remove sometimes. There are some great posts on this. Good detail. Do a search, it will be well worth the minimal effort.
As already said only use motorcraft/beru zd-9 GPs. $9.99 each at autozone. others don't last, swell and burst etc. and make fubar out of your motor. Autolite are reportedly the worst.

 

i had major gp problems, spent about 1500 dolars trying to get it fixed, to the dealer 3 different times and two other private repair guys, nothing worked until i read on of the post about putting a manual button/toggle switch on the glow plug control relay. I have not had a problem since, the best thing i have done.
one of the post around here has a diagram on how to do it. It took all of about one hour to do/ very easy and well worth it

 

Here is the diagram:
http://www.members.shaw.ca/k2pilot/G...%20diagram.jpg

Saigon