528t or rear window defroster relay?

BACKGROUND:

The glow plug relay in my 1984 diesel works fine at startup. But then after I have been driving a while, it will turn on again for about 10 seconds, then turn off, and it may do it again every 15 or 20 minutes. It is a bit random. But is does take a big drain on the alternator when it is on.

I have tried to figure what is wrong with the circuit, but I have not found the cause. At this point, I just want to be done with it.

I want to add a timer relay in the positive (+) wire that feeds the glow plug relay and use it to turn the glow plug relay off anytime after 15 seconds up to a few minutes. (Or would it be better to have the relay on the ground side?). This wire has power anytime the car is on, but does not have power when key switch is in the “start” position and the starter is on.

I like the idea of using a rear window defroster timer relay, but I am not sure which ones have timer circuits in them. One post showed a Nagares relay which has a timer circuit in it, but I have had no luck finding one of them, or even a cross reference to something that seems readily available.

I also like the idea of using the DEI 528T, but I have not been able to find any documentation about that device so I can figure out if it will do what I want or not.

MY QUESTIONS:

Does someone know the make and model of a common American car that uses a timer circuit in its window defogger timer relay? (Would it work?)

Would the DEI 528T work for me?

Anyone have an electronic copy of the manual for a DEI 528T?

I got the manual from the downloads.

Although it is only 1 page, and I had already seen it a bunch of times already (I thought there had to be more to  the manual) it finally makes sense.  Their 3 diagrams sorta, kinda explain how it works.  

So thanks again for the help.