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  #1  
Old 01-09-2014, 01:11 PM
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Function of glow plug relay violet wire

I am trying to get a concensus on what you think is the function of the glow plug relay violet wire (1985 300D). I have a light bulb A connected from violet wire to ground and another bulb B connected from the glow plug output to ground so i can see what's going on without having to deal with volt meters.

When the key is on, bulb B is on (i.e. glow plug getting power), bulb A is off. As I turn the key to crank, bulb A goes on and bulb B stays on (bulb A and B dims due to additional drain from starter motor). When engine fires and I release the key, bulbs A and B go off.

From this observation:

1. Is it behaving correctly?

2. What is the function of the violet wire?

My take from this observation is the violet wire resets the glow plug relay and removes power to the glow plugs once engine starts. Agree, disagree? Other opinions?

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Last edited by funola; 01-09-2014 at 01:39 PM.
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Old 01-09-2014, 01:50 PM
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You got it. The violet wire is the starter signal to the glow relay to stop glowing. In an afterglow relay, it's the trigger to start the afterglow countdown. Cutting the violet wire is a cheap permanent afterglow mod.

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  #3  
Old 01-09-2014, 02:05 PM
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Quote:
Originally Posted by funola View Post

My take from this observation is the violet wire resets the glow plug relay and removes power to the glow plugs once engine starts.
It makes no difference whether the engine starts or not; it's the start attempt that matters. Change "once the engine starts" to "when the key is released from the start position."

Quote:
Originally Posted by funola View Post
As I turn the key to crank, bulb A goes on and bulb B stays on...
Those who insist that the glow plugs do not operate during start are invited to take note.
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Last edited by tangofox007; 01-09-2014 at 02:24 PM.
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Old 01-09-2014, 02:06 PM
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Originally Posted by tangofox007 View Post
It makes no difference whether the engine starts or not. Change "once the engine starts" to "when the key is released from the start position."
You are right.
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Old 01-09-2014, 02:54 PM
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Cut the Violet Wire, run it to a Switch in the dash, then it could off in cold weather for the after glow, and switched back on in the warm weather.

Charlie
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Old 01-09-2014, 03:30 PM
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Quote:
Originally Posted by charmalu View Post
Cut the Violet Wire, run it to a Switch in the dash, then it could off in cold weather for the after glow, and switched back on in the warm weather.

Charlie
Or just pull the wire out of the plug, tape it back and then put it back in spring. A little cleaner IMO. Then again I have that big open button hole on my console.... HMMM
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Old 01-09-2014, 03:57 PM
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Cutting the wire or wiring a switch is the wrong way to do it.

Cutting the violet will give you after glow, after glow time will be the GP relay timeout time. However, cutting the wire or wiring a switch is the wrong way to do it. The right way is to tie it to the temperature of the engine with a thermo switch. It takes a bit of doing but is well worth it. If engine is warm then no after glow otherwise yes. This will prolong the GP life, you do not want the GP to be on for approx 45s every time the engine starts.
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Old 01-09-2014, 04:55 PM
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in my e300 - the afterglow time is controlled by engine temperature sensor wire that goes to the glow plug relay. The violet wire is starter trigger.

so in effect - the system will be live when the GP lamp in on, when cranking and on (depending on temperature) for afterglow.

The afterglow never happens if I start the engine with its temperature above 50C.
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Old 01-09-2014, 10:15 PM
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Quote:
Originally Posted by funola View Post
I am trying to get a concensus on what you think is the function of the glow plug relay violet wire (1985 300D). I have a light bulb A connected from violet wire to ground and another bulb B connected from the glow plug output to ground so i can see what's going on without having to deal with volt meters.

When the key is on, bulb B is on (i.e. glow plug getting power), bulb A is off. As I turn the key to crank, bulb A goes on and bulb B stays on (bulb A and B dims due to additional drain from starter motor). When engine fires and I release the key, bulbs A and B go off.

From this observation:

1. Is it behaving correctly?

2. What is the function of the violet wire?

My take from this observation is the violet wire resets the glow plug relay and removes power to the glow plugs once engine starts. Agree, disagree? Other opinions?
On mine the Violet Wire turns the Glow Plugs on while the Starter is Cranking the Engine.
A white Wire comes up from the small Terminal on the Starter Solenoid and connects to the Violet Wire at the Wire Terminal/Junction Block that is in front of the Battery.

In My case If I disconnect the Violet Wire at the Wire Termnial Block and apply it to the side of the Block that connects to the Battery I can hear the Glow Plug Relay Click on.

In order to test that on a Non-turbo Engine I believe you need to disconnect the Violet Wire down at the Starter Solenoid and apply some Positive Voltage to it.
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Old 01-09-2014, 10:24 PM
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Quote:
Originally Posted by tangofox007 View Post
It makes no difference whether the engine starts or not; it's the start attempt that matters. Change "once the engine starts" to "when the key is released from the start position."



Those who insist that the glow plugs do not operate during start are invited to take note.
I agree the Glow Plugs are on during Cranking (at least on My Year and Model).

The Glow Plugs have the ability to heat the Pre-chamber to a higher temp then the maximum Engine compression can do by merely cranking the; especially during Winter temps.
And, the heat is localized right in the Pre-chamber.
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  #11  
Old 01-11-2014, 11:17 AM
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Quote:
Originally Posted by Diesel911 View Post
On mine the Violet Wire turns the Glow Plugs on while the Starter is Cranking the Engine...............................
Why does the violet wire need to turn the glow plugs on again while the starter is cranking, when the glow plugs are already "on" from the previous event of turning the key to the "on" position?
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  #12  
Old 01-11-2014, 02:33 PM
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Originally Posted by funola View Post
Why does the violet wire need to turn the glow plugs on again while the starter is cranking, when the glow plugs are already "on" from the previous event of turning the key to the "on" position?
For Me I read what is in the Manual and checked the Violet Wire and observed what happend. However, the description in the Manual suffers from some bad wording or bad translation so it is not clear.

When the Key is turned to start it goes past and disconnects the Pre-Glow and reconnects when the Starter is Cranking. If the Pre-glow and Starter were connected together you would start cranking as soon as you turn the Key to Pre-glow

As to the Engineering why I don't know.

What puzzles me is why is there to Relays inside the Glow Plug Relay.
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  #13  
Old 01-11-2014, 02:46 PM
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the relays inside the glow relay are to isolate the circuits. and when those relays fail, the glow relay can actually actuate the starter! (it happened to my car)
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  #14  
Old 01-11-2014, 03:27 PM
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Originally Posted by Diesel911 View Post

When the Key is turned to start it goes past and disconnects the Pre-Glow and reconnects when the Starter is Cranking. If the Pre-glow and Starter were connected together you would start cranking as soon as you turn the Key to Pre-glow
Research the concept known as "Hot in RUN and START."

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