I know I know, there's a lot of glow plug threads and I'm sure the info I'm after is in here somewhere but can't really find a clear answer.

First and this may be a stupid question but my glow plugs cycle for a bit after it starts, should they? Second they always turn on and stay on the same amount of time no matter how warm the engine is, is this normal?

Next wiring a manual glow plug control switch. If cold I might want them to stay on longer, and if the engine is already warmed up, turning them off could save power and wear right? So how to seams simple enough, but do's and don'ts I should consider? How about a temp switch so when already warmed up they don't turn on?

 

i don't really know how, but the GP controller in my 87 senses engine temp and runs them for the full cycle when cold, and barely at all when the engine is hot.
the stickys at the top of the page here have plenty of info, i don't know if you've read through it yet, but it'll give you a little more background knowledge to work from.
for them to cycle after starting is normal, but for some reason i never hear mine cycle, though i know they stay lit for a short time after the light goes out.

as for a manual switch, just need to mount a pushbutton on the dash somewhere and wire it up to control the big relay on the GP controller that looks like a starter solenoid. or use a starter solenoid for it if you prefer.
but IMO, the system is working, don't screw with it. personally, i like my factory GP controller, it just does what its supposed to do

 

I have two truck's....
One with the manual button, works great, I can cycle the plugs whenever I want, on cold days, I cycle them twice for 10 seconds, before starting.
My other truck, has the controller, it does click after starting for another 4 or 5 times.Doesn't seem to stay on long enough on the second heating, so I may change it over to the push button style for more control over it.
Hope that helped.

 

A glow plug's electrical resistance goes up as it gets hotter.
On the new style system, the controller senses the resistance to ground through the glow plugs to determine whether the engine is warm or cold. This is why one or two burned out glow plugs make the controller short-cycle: burned out plugs mean the controller sees higher resistance, and thinks the engine is warm when it's cold.