I believe the issues with the 6.9 System was with the "dumb" controller, not the plugs. The 6.9 controller is basically just an on/off controller that runs the plugs. It's supposed to sense coolant temp also, and not run above a certain temp. They have a habit of failing and staying or, or will just run the plugs randomly. I've read may questions of why does my WTS light come on while I'm driving down the road.
I'm not sure about that. On restart, the plugs sometimes come on but don't stay on as long.
I haven't ever noticed WTS come on when driving, but Ford put it where you cant even see it (or the "ENGINE" light!) when driving, because the steering wheel completely blocks it from view during normal sitting posture. It does come on a few times when first idling until the cylinders/glow plugs get to a certain temp. And as loud as this thing is, it might be hard to hear. Putting in a 12v buzzer tied to the WTS light might not be a bad idea if running the controller like I am.
I think my 87 6.9 with the 7.3 system did the same though as I recall. Maybe I'm wrong on that though. It's been about 10 months since I drove it and I never paid much attention to that after a couple years of driving it, as long as it clicked on pre-starting.
Supposedly, the new controllers made today are solid state and fix the problem of old electro-magnetic ones.
Mine definitely has the old style, you can tell just by looking. It has a ********* cylindrical piece that sticks outward from the pigtail, plugged into the middle of it:
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The new ones don't have that area:
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DieselRX has one for under $70 and all 7 reviews are 5/5:
https://www.amazon.com/DieselRx-DRX01003-Glow-Plug-Controller/dp/B00TOZ9CUG