1996 e300 glow plug relay

[scottdarling122]

hello all i have a 1996 e300d i just replaced all of the glow plugs because one of the old ones were bad figured might as well do it right and change them all since the intake has to come off to get at them.So i changed them now it starts great nice and smooth glow plug light comes on for 7 secs or so then shuts off after its warmed up and i go to start it again after i shut it off light comes on for a few seconds and starts great still.Heres my problem when i start it and drive it for a few minutes the glow plug light comes back on and stays on for a few minutes then shuts off.Nowing how bad it is for glow plugs to stay on for extened periods of time i brought it home to investigate .I checked the impedance of all the glow plugs before i put them in they were matched i checked the impedance between the glow plug connector and the glow plugs the connector that hooks up to the relay that is to the glow plugs turned out to be fine. So hooked up a test light to the output of the relay with the glow plug plug still plugged in and i saw over 12 volts so the plugs are getting power.I also tested the pos 14 volt input connection and saw 14 volts.I took the relay cover off and turned the car on relay engaged then disengaged after 7 seconds or so then when i started the car it re engaged So i shut the car off the next 3 times i started the car the relay engaged and stayed engaged and nver relased until i shut the car off.Oh yeah the battery is new and also before i changed the glow plugs the glow plug light would come on the same way but would have to drive it longer for it to come on.Do i need a new relay if any one could help would be greatly apreciated also if anyone know the wiring for the control wires on the relay would also help so i can test

[Parrot of Doom]

The glow plugs remain on for a period of 1 minute once the engine has started. This is quite normal. The GP light on the dash should not be lit.

A lit glow plug light on the dash after the engine has started signifies that one or more glow plugs (or associated circuitry) is faulty.

The relay is a simple circuit, before you consider replacing it open it up and check that there are no obvious faults, like a melted fuse, blackened component, or dry joints:

[scottdarling122]

thank you for responding i will go out and check it out with your new information.But why does the light come back on a few minutes after driving and stays on for a couple minutes i dont want to risk burning up the glow plugs.I guess i should check to see if they are turning back on or if its just the light turning on thanks again if you have any more input i would love to hear it thanks alot have a great day

[scottdarling122]

Just tested it glow plug stays on even when light goes off then after i start the car remains on for over 2 minutes at that time i shut the car off so i dont damage the plugs i could have sworn the plugs should only come on for 7 seconds and then shut off and only come on when light is on

[Parrot of Doom]

You probably have a faulty GP relay. Take it out and investigate.

I may actually be wrong about them staying on for 1 minute - it could be 7 seconds. I'd have to check mine to be sure.

[scottdarling122]

could it be the GLOW PLUG THERMO TIME SWITCH would that make the relay stay engaged if it were to go bad